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diff --git a/.gitattributes b/.gitattributes new file mode 100644 index 0000000..d7b82bc --- /dev/null +++ b/.gitattributes @@ -0,0 +1,4 @@ +*.txt text eol=lf +*.htm text eol=lf +*.html text eol=lf +*.md text eol=lf diff --git a/LICENSE.txt b/LICENSE.txt new file mode 100644 index 0000000..6312041 --- /dev/null +++ b/LICENSE.txt @@ -0,0 +1,11 @@ +This eBook, including all associated images, markup, improvements, +metadata, and any other content or labor, has been confirmed to be +in the PUBLIC DOMAIN IN THE UNITED STATES. + +Procedures for determining public domain status are described in +the "Copyright How-To" at https://www.gutenberg.org. + +No investigation has been made concerning possible copyrights in +jurisdictions other than the United States. Anyone seeking to utilize +this eBook outside of the United States should confirm copyright +status under the laws that apply to them. diff --git a/README.md b/README.md new file mode 100644 index 0000000..434e718 --- /dev/null +++ b/README.md @@ -0,0 +1,2 @@ +Project Gutenberg (https://www.gutenberg.org) public repository for +eBook #62521 (https://www.gutenberg.org/ebooks/62521) diff --git a/old/62521-0.txt b/old/62521-0.txt deleted file mode 100644 index 41f32ec..0000000 --- a/old/62521-0.txt +++ /dev/null @@ -1,3870 +0,0 @@ -The Project Gutenberg EBook of Links With the Past in the Plant World, by -Albert Charles Seward - -This eBook is for the use of anyone anywhere in the United States and most -other parts of the world at no cost and with almost no restrictions -whatsoever. You may copy it, give it away or re-use it under the terms of -the Project Gutenberg License included with this eBook or online at -www.gutenberg.org. If you are not located in the United States, you'll have -to check the laws of the country where you are located before using this ebook. - -Title: Links With the Past in the Plant World - -Author: Albert Charles Seward - -Release Date: June 29, 2020 [EBook #62521] - -Language: English - -Character set encoding: UTF-8 - -*** START OF THIS PROJECT GUTENBERG EBOOK LINKS WITH PAST IN PLANT WORLD *** - - - - -Produced by Tom Cosmas - - - - - - - - - The Cambridge Manuals of Science and - Literature - - - - - LINKS WITH THE PAST IN - THE PLANT WORLD - - - - - CAMBRIDGE UNIVERSITY PRESS - - London: FETTER LANE, E.C. - - C. F. CLAY, Manager - - - - - Edinburgh: 100, PRINCES STREET - London: H. K. LEWIS, 136, GOWER STREET, W.C. - Berlin: A. ASHER AND CO. - Leipzig: F. A. BROCKHAUS - New York: G. P. PUTNAM'S SONS - Bombay and Calcutta: MACMILLAN AND CO., Ltd. - - - -_All rights reserved_ - -[Illustration: _Sequoia magnifica_ Knowlton, in the Yellowstone -National Park. (From a photograph kindly supplied by Prof. Knowlton.) -See p. 104.] - - - - - LINKS WITH THE - PAST IN THE - PLANT WORLD - - - BY - - A. C. SEWARD, - - M.A., F.R.S. - - Professor of Botany in the - University of Cambridge - - Cambridge: - at the University Press - - 1911 - - -Cambridge: - -PRINTED BY JOHN CLAY, M.A. AT THE UNIVERSITY PRESS - - -_With the exception of the coat of arms at the foot, the design on -the title page is a reproduction of one used by the earliest known -Cambridge printer, John Siberch, 1521_ - - - - -PREFACE - - -MY object in writing this book is primarily to call attention to some -of the many questions which are raised by an enquiry into the relative -antiquity of existing plants, and to illustrate the nature of the -evidence afforded by the records of the rocks. One may agree with the -dictum, 'There is but one art--to omit,' but to practise this art is -often a difficult task. While fully conscious of the incompleteness of -the treatment of the subjects dealt with in these pages, and of defects -in the method of presentation, I hope that I may succeed in attracting -some of my readers who are already interested in living plants to the -study of plants of former ages. - -I am greatly indebted to my colleague Dr C. E. Moss for reading the -proofs and for many valuable suggestions. I wish to thank Mr and Mrs -Clement Reid, Prof. MacDougal of the Arizona Desert Laboratory, Prof -Campbell of Stanford University, Prof F. H. Knowlton of the United -States National Museum, Washington, Mr A. G. Tansley, Prof Yapp, and Mr -W. R. Welch for photographs which they have allowed me to reproduce. As -on many previous occasions, I am indebted to my wife for contributing -drawings. - -A. C. SEWARD. - -Botany School, Cambridge. _July 1911._ - - - -The numbers in brackets interspersed in the text refer to the -Bibliography at the end of the volume. - - - - -CONTENTS - - - PAGE - -Preface vii - - -CHAP. - - I. Introductory: the Longevity of Trees, etc. 1 - - II. The Geographical Distribution of Plants 15 - - III. The Geological Record 39 - - IV. Preservation of Plants as Fossils 56 - - V. Ferns; their Distribution and Antiquity 71 - - VI. The Redwood and Mammoth Trees of California 95 - - VII. The Araucaria family 106 - -VIII. The Maiden Hair Tree 121 - - Bibliography 134 - - Index 139 - - * * * * * - - -_Links with the Past_ - -ERRATUM - -Page 78. Omit lines 5, 6, and 7, from "One" to "but" inclusive. - - Transcriber Note: This correction has been applied. Here is the - original sentence:-- - - One filmy species of Todea is represented in the British flora - by _Todea radicans_ in the Killarney district of Ireland; but - the maximum development of the genus is in New Zealand. - - - * * * * * - - - - -CHAPTER I - -INTRODUCTORY: THE LONGEVITY OF TREES, ETC. - - 'Believe me who have tried. Thou wilt find something more in - woods than in books. Trees and rocks will teach what thou canst - not hear from a master.' - St Bernard. - - -The recent publication in the daily press of instances of human -longevity under the heading 'Links with the Past' prompted a comparison -between the length of time represented by the duration of a tree -and the lifetime of a human being. The comparison of single lives -suggested the further step of contrasting the antiquity of the oldest -family-histories with the remoteness of the period to which it is -possible to trace the ancestry of existing members of the plant kingdom. - -My primary object in these pages is not to deal with familiar cases -of longevity in trees, but to consider in the first place some of the -problems connected with the origin of the present British flora, and -then to describe a few examples of different types of plants whose -ancestors flourished during periods of the earth's history long ages -before the advent of the human race. - -In dealing with plants of former ages we are confronted with the -difficulty of forming an adequate conception of the length of time -embraced by geological periods in comparison with the duration of the -historic era. Some of the 'Selections from the Greek Papyri' recently -edited by Dr Milligan (Cambridge 1910) refer to common-place events -in terms familiar to us in modern letters: we forget the interval of -2000 years which has elapsed since they were written. Similarly, the -close agreement between existing plants and species which lived in -remote epochs speaks of continuity through the ages, and bridges across -an extent of time too great to be expressed by ordinary standards of -measurement. Terms of years when extended beyond the limits to which -our minds are accustomed cease to have any definite meaning. While -there is a certain academic interest in discussions as to the age of -the earth as expressed in years, we are utterly unable to realise the -significance of the chronology employed. After speaking of the futility -of attempting to introduce chronological precision into periods -so recent as those which come into the purview of archaeologists, -Mr Rice Holmes suggests a method better adapted to our powers. He -says--'Ascend the hill on which stands Dover Castle, and gaze upon -Cape Grisnez, let the waters beneath you disappear; across the chalk -that once spanned the channel like a bridge men walked from the white -cliff that marks the horizon to where you stand. No arithmetical -chronology can spur the imagination to flights like these(1).' On the -other hand, the use in some country districts in Britain of spindles -almost identical with instruments used in spinning by the ancient -Egyptians, and similar survivals described by the author of a book -entitled _The Past in the Present_(2), bring within the range of our -vision an early phase of the historic era. The rude implements still -fashioned by the flint-knappers of Brandon in Suffolk connect the -present with the Palaeolithic age. Measured from the standpoint of -historic reckoning, survivals from prehistoric days appeal to us as -persistent types which have remained unchanged in a constantly changing -world. - -In one of his essays Weismann quotes an old German saying with regard -to comparative longevity, which asserts that 'a wren lives three years, -a dog three times as long as a wren' and so on in a regularly ascending -series: the life of a deer is estimated at three times that of a crow -and an oak three times that of a deer, which means that, computed -on this basis, an oak lives nearly 20,000 years(3)! This fanciful -illustration of the relative longevity of an oak is the expression of -a truth, namely the superiority of trees over animals in regard to -the duration of life. As a seventeenth-century translator of Pliny's -_Natural History_ writes, 'In old times trees were the very temples -of the gods: and according to that antient manner, the plaine and -simple peasants of the country, savouring still of antiquity, do at -this day consecrate to one God or other, the goodliest and fairest -trees that they can meet withal.' Oaks growing in Pliny's day in the -Hercynian forest are said to have been there 'ever since the creation -of the world(4).' Sir Joseph Hooker, in an account of some Palestine -oaks, gives a drawing of a famous tree at Mamre, known as Abraham's -Oak, which is supposed to mark the spot where the Patriarch pitched -his tent(5). Examples such as these, though of no scientific value, -serve to illustrate the well-founded belief in the extraordinary -longevity of trees. In the absence of evidence to the contrary, it -would be rash to deny the possibility that William the Conqueror's Oak -in Windsor Forest, described by Loudon in his _Arboretum Britannicum_ -and mentioned by later writers, may be a survival from the reign of -the king whose name it bears. Although it is seldom possible to state -with confidence the exact age of old oaks and yews famed for length -of days, there can be no doubt as to the enormous antiquity of -many of our trees whose years are 'sacred with many a mystery.' The -section of a trunk of one of the mammoth trees of California (_Sequoia -gigantea_) exhibited in the Natural History department of the British -Museum, shows on its polished surface 1335 concentric rings denoting -successive increments of wood produced by the activity of a cylinder -of cells situated between the hard woody tissue and the bark. It is -generally assumed that each year a tree produces a single ring, though, -as is well known, an estimate of age calculated on this assumption -cannot be regarded as more than an approximation to the truth. If this -giant tree, which was felled in 1890, was then 1335 years old, it had -already reached an age of over two centuries when Charlemagne was -crowned Emperor at Rome. The concentric rings on a tree trunk owe their -existence to certain structural differences between the wood formed -in the spring and in the late summer. In Sequoia, as in other members -of the great class of cone-bearing trees, the wood is composed of -comparatively narrow elements which serve to carry water from the roots -to the branches and leaves. As spring succeeds winter the inactivity of -the plant-machine is followed by a period of energetic life; opening -buds and elongating shoots create a demand for a plentiful supply of -ascending sap, and in response to this the tree produces a fresh -cylinder of wood composed of relatively wide conducting tubes. After -the first rush of life is succeeded by a phase of more uniform and -gentler activity, the demand for water becomes less exacting and the -wood which is formed during the rest of the growing season consists of -narrower water-pipes. A period of rest ensues, until in the following -spring new layers of larger tubes are laid down in juxtaposition to -the narrower elements of the latest phase of the preceding summer. -This alternation of larger and smaller tubes produces the appearance -of concentric rings on a cross-section of a tree. It is not the pause -in the active life of the plant which is responsible for the effect -of rings, but the fact that the wood produced immediately before and -immediately after the pause is not structurally identical. In trees -grown under the more uniform conditions of certain tropical regions, -the annual rings are either feebly developed or absent; for example, in -some Indian oaks the wood shows no concentric rings of growth. - -Stated in general terms, rings of growth in the wood of a tree are -the expression of a power possessed by the plant of regulating the -structure of its component elements in response to the varying nature -of the external stimuli. In certain circumstances, for example after -the destruction of the young buds by caterpillars, the tree makes a -special effort to repair the loss by producing a new set of shoots. -This may be recorded by the occurrence of two concentric rings in one -season. An extreme instance of departure from the normal has recently -been described(6) in which a tree of _Theobroma cacao_ (the cocoa -tree), planted in Ceylon in the summer of 1893 and felled in January -1901, after a life of just over 7 years, was found to have 22 rings in -its stem. In this case the tree shed its leaves three times a year, and -each break in the uniformity of its vital activities was registered -by the apposition of what under ordinary conditions are spoken of as -spring and late-summer wood. At Aden trees stated by natives to be -very old showed only five or six rings of wood, a fact connected with -the almost complete lack of rain and with the uniform conditions of -existence. - -The degree of accuracy to be allowed to estimates of age founded on -the number of 'annual' rings is, however, of secondary importance in -comparison with the enormously greater hold on life possessed by trees -as contrasted with the higher animals. Early in the nineteenth century -the Swiss botanist A. P. de Candolle expressed the opinion that trees -do not die from senile decay, but only as the result of injury or -disease. Trees are constructed on a plan fundamentally different from -that underlying the structure of the highly complex human organism, -and are thus endowed with a sort of potential immortality. It has -been suggested that some of the large corals in the Red Sea which -are still tenanted by living polyps may have been growing in the days -of the Pharaohs. The coral polyp represents the growing portion of a -lifeless mass of rock which is constantly extended by the activity of -the organism at the summit of each branch. Between a coral-reef and a -tree there are many essential differences, but a rough analogy may be -recognised. A tree, unlike the higher animals, does not reach a stage -at which the whole of its substance attains a condition of permanence -and fixity. It consists of a complex branching-system in which each -shoot increases in length by virtue of the youthful vigour of its apex: -to a large extent the tree as a whole consists of lifeless material -incapable of further growth, as is the case of the older portions of -a coral-reef; but the regular increase in girth of the trunk and its -branches demonstrates that this comparison is only partially true, and -that the power of growth in a tree is not confined to the extremities -of the youngest shoots. The tip of every twig is composed of minute -cells endowed with a potentiality of development like that which -characterises the embryonic tissues of a seedling just emerged from the -seed. In the course of its growth, each branch, by means of its living -and dividing cells, contributes to the several parts of the complex -mechanism of the tree. While the greater number of cells acquire a -permanent form and lose the power of further development, there -remains a cylinder of cells endowed with perpetual youth. This cylinder -of living cells, known as the cambium, extends between the wood and -bark from one end of the tree to the other: by its periodic activity it -adds new layers of tissue each year and thus, by increasing the amount -of conducting tubes for the transport of water and for the distribution -of elaborated food, it enables the tree to respond to the increasing -demands which are the necessary accompaniment of increasing size. It -has already been pointed out that in the spring when the sap flows most -vigorously the cambial cylinder produces larger tubes, and afterwards -when the tree settles down to its normal life, these are succeeded by -narrower and stronger tubes. These later formed elements serve also -an important mechanical purpose; by the strength of their walls they -increase the supporting power of the tree and enable it to sustain the -added burden of the annual increase in the weight and extent of its -spreading branches. - -It is the persistence of permanently juvenile tissue in certain regions -of a tree, together with the remarkable power of repairing injuries -and shedding effete parts, that constitute some of the most striking -contrasts between the higher animals and plants. The embryo oak in the -earlier stages of development consists entirely of actively growing -cells; by degrees differentiation of the embryonic tissues results -in the localisation of regions of cell-production at the tips of -the elongating stem and root. These apical groups of cells are, in -fact, portions of the embryonic organism which persist so long as the -plant lives. This continuity between the growing tip of an old oak -stem and the cells of the undifferentiated embryo affords one of the -most remarkable examples in nature of a link between the past and the -present. - -If we pass beyond the stretch of time represented by the life of -a single tree, a few successive generations suffice to carry our -retrospect back to the days when forests of oaks, birches, and other -trees impeded the progress of the Roman invaders, and, a stage farther -back, to the age of Neolithic man whose remains are occasionally -found in our heaths and moors and in the submerged forests round our -coast. The blocks of oak and beech, some of which are as sound as when -first felled, recently discovered below the foundations of parts of -Winchester Cathedral constructed at the end of the twelfth or in the -opening years of the thirteenth century, are relics of Norman forests. -In the course of some excavations at Brigg in Lincolnshire in 1886 a -dug-out boat was found nearly 50 feet long and from 4 to 5 feet in -breadth. The stem of the oak from which the canoe had been fashioned -shows no sign of branching for a length of over 40 feet, a fact which -points to the growth of the tree in a forest where the race for light -induced the development of clean columnar stems. The Brigg 'dug-out,' -now in the Hull Museum, was discovered in an old alluvial valley of the -Ancholme river, formerly connected with the Humber, and it may be that -it was used by Neolithic man as a ferry for river-service(7). - -From the period claimed by archaeologists we pass by gradual stages -into the domain of the geologist. As Huxley wrote, 'when even the dim -light of Archaeology fades, there yet remains Palaeontology, which... -has brought to daylight once more the exuvia of ancient populations, -whose world was not our world, who have been buried in river beds -immemorially dry, or carried by the rush of waters into caves, -inaccessible to inundation since the dawn of tradition(8).' The length -of time represented by a succession of long-lived individuals of the -same species becomes enormously extended when we pass to the history -of families, and disinter from the sediments of other ages the remains -of extinct types. As we descend the geological series familiar types -gradually disappear, and through a succession of changing floras we -penetrate to the fragmentary records contained in the older rocks until -the absence of documents sets a limit to our quest. - -[Illustration: Fig. 1. _Pinus sylvestris_ Linn, in the Black Wood of -Rannoch. (Photograph by Mr A. G. Tansley.)] - -The Scots pine shares with the oak, the beech, the aspen, the yew, -and several other trees the right to be included in the native -flora of Britain. In the peat-beds of Scotland even up to 3000 feet -above sea-level the stumps of pines occur in abundance, and in many -places recent researches have revealed the occurrence of successive -forests of pines, oaks, and spruces separated from one another by -the accumulations of swampy vegetation(9). The spruce fir has long -ceased to be a member of the British flora, but in a few localities in -the Scottish Highlands patches of primeval pine forests remain. The -accompanying photograph (Fig. 1), taken by my friend Mr A. G. Tansley, -in the Black Wood of Rannoch in north-west Perthshire, shows a few -trees of _Pinus sylvestris_ growing in their native soil: the form of -the older tree (_A_) suggests comparison with that of a well-grown -beech such as we are familiar with in English plantations. This -spreading dome-shaped habit seems to be a peculiarity of the Highland -tree, and is one of the characters which have led some botanists to -regard it as a variety (_Pinus sylvestris_ var. _scotica_) of the -ordinary Scots pine. Though it is doubtful if any relics of primeval -pine woods are left in England, abundant evidence of the former -existence of the Scots pine is afforded by the submerged forests -exposed at low-tide on many parts of the English and Welsh coasts and -at the base of some of the English peat moors. During the construction -of the Barry docks on the north coast of the Bristol Channel a -few years ago, the exposed sections of peat and forest beds were -investigated by Dr Strahan and by Mr Clement Reid. There is evidence of -a subsidence of the land to an extent of 55 feet since the formation of -the lower peat-beds containing oak, hazel, willow, and other trees. The -pine, unknown in Wales during the historic period, was recognised in -the Barry cutting. The occurrence of a polished flint implement assigns -a date to the uppermost portion of this old land-surface(10). - -It is impossible within the limits of a small volume to discuss in -detail the evidence furnished by the records of the rocks as to the -relative antiquity of the different constituents of the present -vegetation of Britain. In later chapters a few selected plants are -described which are pre-eminently ancient types. Before passing to the -consideration of the data on which the geological history of plants is -based, brief reference may be made to one of the most interesting and -difficult problems of botanical research, namely the history of the -British flora. - - - - -CHAPTER II - -THE GEOGRAPHICAL DISTRIBUTION OF PLANTS - - 'No speculation is idle or fruitless that is not opposed to truth - or to probability, and which, whilst it co-ordinates a body of well - established facts, does so without violence to nature, and with a due - regard to the possible results of future discoveries.' - - Sir Joseph Hooker. - - -In the vegetation of the British Isles the leading _rôle_ is played -by that large group to which the term Flowering Plants is frequently -applied. This group, including the two sub-divisions Dicotyledons -and Monocotyledons, is known by the name Angiosperms, a designation -denoting the important fact that the seeds are developed in an ovary -or protective seed-case (ἁγγειον, a vessel or box). The fact that -these highly elaborated products of development made their appearance, -so far as we know, at a comparatively late stage in the history of -the plant-world, attests their efficiency as a class and demonstrates -the rapidity with which they have overspread the surface of the earth -as successful competitors in the struggle for existence. As Darwin -wrote in a letter to Sir Joseph Hooker in 1881, 'Nothing is more -extraordinary in the history of the vegetable kingdom, as it seems to -me, than the _apparently_ very sudden or abrupt development of the -higher plants(11).' In another letter (1879) to the same friend we -read, 'The rapid development as far as we can judge of all the higher -plants within recent geological times is an abominable mystery(12).' -Making allowance for the probability, or indeed certainty, that the -imperfection of the geological record tends to exaggerate the apparent -suddenness of the appearance of this vigorous class, and allowing for -the fact that our knowledge of the records of the rocks in which the -highest plants first occur is very incomplete, we cannot escape from -the conclusion that this recently evolved group spread with amazing -rapidity. Various reasons may be suggested in explanation of the -dominant position which the Angiosperms hold in the floras of the -world. As an instance of their rapid increase during the Cretaceous -epoch[1], the period which has furnished the earliest satisfactory -records of Flowering Plants, the following statement by an American -writer may be quoted:--'The rapidity with which it [_i.e._ the group of -Flowering Plants] advanced, conquering or supplanting all rivals, may -be better understood when we remember that it forms 85% of the flora -of the Dakota group '; that is a series of sedimentary rocks in Dakota -referred by geologists to the middle of the Cretaceous period(13). In -the Wealden rocks of England, which are rich in the remains of Lower -Cretaceous plants, no undoubted Flowering Plant has so far been found. - -[1] For the position of the Cretaceous and other systems in the -geological series, see the table on page 42. - -The more efficient protection of the ovules, the germs which, after -fertilisation, become the seeds, the extraordinary variety in the -floral mechanisms for assisting cross-pollination, the arrangements -for nursing the embryo, and the structural features of the wood in -relation both to rapid transport of water and to the storage of food, -are factors which have probably contributed to the success of the -Angiosperms. The degree of weight to assign to each contributing cause -cannot as yet be satisfactorily determined, but the general question -raised by the recent origin of these latest products of evolution -offers a promising field for work. While admitting our inability -at present to do more than suggest possibilities, we may encourage -research by speculation. - -The members of the Vegetable Kingdom placed next to the Flowering -Plants are the Gymnosperms or naked-seeded (γυμνὁς, naked) plants, -including (i) the Conifers, _e.g._ pines, firs, larches, the yew, -etc., (ii) a small group of plants known as the Cycads, whose -existing members, now almost confined to a few tropical regions, are -the descendants of a vigorous race represented by many species in the -floras of the Mesozoic epoch. A third sub-division of the Gymnosperms, -the Ginkgoales, is represented by a single survivor, which is described -in a later chapter as one of the most remarkable links with the past in -the plant kingdom. - -The Gymnosperms are geologically very much older than the Angiosperms. -Members of this class played a prominent part in the vegetation of -the Coal age and it is certain that they existed in the still older -Devonian period. The only other group to which reference is made in -later chapters is that of the Ferns, one of the sub-divisions of a -large class known as the Vascular Cryptogams or Pteridophyta. These -plants, like the Gymnosperms, are represented in the oldest floras of -which recognisable remains have been preserved. The main groups of the -vegetable kingdom, founded on existing plants, are distinguished by -well-defined differences; they are comparable with separate twigs of a -tree springing from larger branches and these again uniting below in -a common trunk. The vegetation of to-day represents only the terminal -portions of the upper branches. As we descend the geological series, -records of extinct types are found which enable us either to trace -the separate branches to a common origin or to recognise a convergence -towards a common stock. Were a botanist to find himself in a forest of -the Coal age he would experience great difficulty in assigning some -of the plants to their systematic position: characters now regarded -as distinguishing features of distinct groups would be met with in -combination in a single individual. It is by the discovery of such -generalised types, which serve as finger-posts pointing the way to -lines of evolution, that the student of pre-existing plants has been -able to throw light on the relative antiquity of existing forms, and -to trace towards a common ancestry plants which now show but little -indication of consanguinity. - -Confining our attention to the dominant group of plants in the British -flora, namely the Flowering Plants, we may profitably consider the -question, though we cannot satisfactorily answer it,--which members of -this group are entitled to be regarded as the most ancient inhabitants? -The past history of our native plants, and their geographical range, -not only in the British Isles but on the Continent of Europe, are -subjects well worthy of the attention of field-botanists whose -interests are apt to be confined within too narrow bounds. There are -numerous problems relating to the composition of the present vegetation -of Britain which might be discussed in reference to the relative -antiquity of plants; but in a single chapter it is impossible to do -more than call attention to certain considerations which are frequently -overlooked by students of British species. - -It is customary to speak of the British flora as consisting for the -most part of species introduced into this country by natural means, -while some plants owe their introduction to human agency or are -'escapes' from cultivation. It is by no means an easy task in some -instances to decide whether a species is native or introduced, but -in some cases, a few of which are mentioned, there is no doubt as to -the alien nature of the plants. The term 'native' needs a word of -explanation. It is not intended to convey the idea that a plant so -designated came into existence on British soil and spread thence to -other regions; but by native species we mean such as have reached this -country by migration from other lands, or it may be in some instances -have actually originated in this part of Europe. One of the best known -aliens in Britain is the American water-weed, _Elodea canadensis_ -(or _Anacharis alsinastrum_), which was discovered about sixty years -ago in a canal near Market Harborough in Leicestershire(14). In all -probability this North American species was introduced into England -with timber. Once established, it spread through the waterways with -alarming rapidity and became a serious pest. Elodea affords an -admirable instance of the serious interference with the balance of -Nature by the introduction of a new competitor into an environment -conducive to vigorous development. Another foreign water-plant, -_Naias graminea_, for the importation of which Egyptian cotton -may be responsible, has been recorded from the Reddish canal near -Manchester(15). This African and Asiatic species occurs in Europe -only as a colonist; it is said to have been introduced into Italy -with East Indian rice. A more recent case of alien immigration due to -unintentional human agency is that of _Potamogeton pennsylvanicus_, -a pond-weed of Canada, the United States, Jamaica, and elsewhere. -Specimens of this species were first noticed in 1907 in a canal near -Halifax close to the effluent from a cotton mill. Since its discovery -the plant has slightly extended its range. It is suggested by Mr -Bennett, who first identified the alien, that its fruits were brought -to this country in goods from the United States(16). - -Of the introduction of these and other foreign plants we have -satisfactory records; but there are many others which may owe their -presence to man's agency, though we have no information as to their -arrival. - -It has long been recognised that several members of the British flora -are related to Scandinavian species. The Scandinavian flora, as Sir -Joseph Hooker says in his well-known paper on the 'Outlines of the -Distribution of Arctic plants,' 'not only girdles the globe in the -Arctic Circle, and dominates over all others in the North Temperate -Zone of the Old World, but intrudes conspicuously into every other -temperate flora, whether in the northern or southern hemisphere, or on -the Alps of tropical countries'(17). The view generally held is that -during the Glacial period this Arctic flora was driven South, and aided -by land-bridges, which were afterwards submerged, many of the northern -migrants found a more congenial home in Britain. It is however by no -means improbable that this conclusion may have to be considerably -modified. Mr and Mrs Reid, as the result of their careful analysis -of the Pre-Glacial Flora of Britain, express the opinion that 'the -pre-glacial plants suggest climatic conditions almost identical with -those now existing, though slightly warmer' (27, 2). It is noteworthy -that the list of plants given in their paper does not include any -typical Arctic species. The occurrence on the mountains of Scotland -and elsewhere of such plants as _Silene acaulis_, _Dryas octopetala_, -_Saxifraga oppositifolia_ and other Saxifrages, _Rubus chamaemorus_ -(the Cloudberry), and the dwarf Birch illustrate the Arctic-Alpine -element in our flora. - -The opinion is held by many Swiss botanists that their Alpine species -have in large measure been derived from non-glaciated parts of the -Pyrenees, that is from a region which was presumably able to retain its -flora at a time when more northern lands were exposed to extreme Arctic -conditions. My friend Dr Moss believes that some of the so-called -Scandinavian plants came to Britain from Central Europe after the -retreat of the ice; if this view is correct it means that some at least -of our Arctic-Alpine plants reached these islands by a southern rather -than by a northern route. - -Interesting examples of far-travelled northern plants recently -described by Professor Engler of Berlin afford additional illustrations -of the general principles enunciated many years ago by Sir Joseph -Hooker. A species of flowering Rush, _Luzula spicata_ var. _simensis_, -occurs at an altitude of 3600 metres in Abyssinia and on Kilimanjaro. -_Luzula spicata_ is found in the whole of the Arctic and Subarctic belt -in Scotland, Auvergne, the Jura mountains, and elsewhere. The species -probably began its career in the northern hemisphere where it grew -abundantly on the higher ground in the Arctic Circle: it eventually -travelled along the North American Andes and appeared in Mexico under a -guise sufficiently distinct to warrant the use of another name, _Luzula -racemosa_. In an eastern direction it reached the Himalayas and is -represented in Abyssinia by a closely allied form. From Abyssinia to -Kilimanjaro _Luzula spicata_ 'had to travel a long distance; but it is -not impossible that it either still exists or has existed previously on -a few of the high mountains between Abyssinia and Kenia, from which, -having advanced to the Kilimanjaro, it again produced new forms.... -At any rate, it is impossible to do without distribution of seeds of -alpine plants by air-currents or by birds from one mountain to the -other in explaining the history of distribution'(18). - -The majority of British plants are identical with species in Central -and Northern Europe: of these, some are among the most widely spread -English species, _e.g._ the Daisy and Primrose, while others, such as -the Oxlip (_Primula elatior_), are confined to the Eastern counties, -and others, such as the Cheddar Pink (_Dianthus caesius_), are -restricted to Western counties. - -Before considering a small section of the British flora which is the -most interesting from the point of view of origin, a short digression -may be allowed in order to call attention to the importance of a -branch of science which Darwin spoke of as 'that grand subject, that -almost keystone of the laws of creation, geographical distribution,' -and in 1847 referred to as 'that noble subject of which we as yet -but dimly see the full bearing.' It was largely as the results -of his study of distribution in the Galapagos Islands that Darwin -determined to 'collect blindly every sort of fact which bears anyway -on what are species.' The acceptance of the view 'that each species -was first produced within a single region'(19), raises the subject of -geographical distribution to a far higher plane than it occupied in -pre-Darwinian days. Although most people are familiar with some of -the commoner means by which plants are able to colonise new ground -through the adaptation of their fruits and seeds to various methods of -transport, the conception of a plant as a stationary organism tends -to prevent due allowance being made for the comparative facility with -which, in the course of successive generations, a species is able to -wander from place to place. The individual animal is endowed with -powers of locomotion enabling it to seek new feeding-grounds and to -avoid enemies; but with the exception of some of the simplest forms a -plant cannot move--'le matin la laisse où la trouve le soir.' - -The rate of travel may or may not be rapid, but in a comparatively -short time, if the conditions are favourable, a tree may spread over -a wide area. Mr Ridley, Director of the Botanic Gardens, Singapore, -writes as follows in reference to the rate of travel of one of the -common Malayan trees (_Shorea leprosula_), which bears winged fruits -particularly well adapted to wind-transport: 'If we assume that a tree -flowers and fruits at 30 years of age and the fruits are disseminated -to a distance of 100 yards, that the furthest fruits always germinate -and so continue in one direction, it will be seen that under such most -favourable circumstances the species can only spread 800 yards in 100 -years, and would take 58,666 years to migrate 100 miles'(20). - -There is, however, one type of distribution--what is called -discontinuous distribution--to which special attention should be -directed on account of its intimate association with questions -relating to the past history of living organisms. Many examples might -be quoted from both the animal and plant kingdoms in support of the -view that discontinuous distribution is a criterion of antiquity. When -identical or very nearly identical plants occur in regions separated -from one another by areas in which the particular species is unknown, -the inference is either that the surviving individuals are remnants -of a large number formerly distributed over a wider continuous area, -or that in the course of evolution similar conditions in widely -separated areas led to the production of identical types. The former -view is much the more probable: it is consistent with the conclusions -arrived at on other grounds as to the connexion between discontinuous -distribution and ancient lineage. The explanations of the widespread -occurrence among different races of similar objects or legends afford -an analogous case. As Dr Andrew Lang points out in _Custom and Myth_, -it is held by some students that the use of the bull roarer--to cite a -specific instance--by different peoples denotes descent from a common -stock, though he considers the more probable explanation to be that -similar minds, working with simple means towards similar ends, might -evolve the bull roarer and its mystic uses anywhere. - -The Cedars of Lebanon afford an interesting example of discontinuous -distribution. They illustrate how a species, which may be assumed to -have originated in one region, in the course of its wanderings may -undergo slight changes until, at a later stage when the plants have -disappeared from parts of the once-continuous area, the remaining -outlying groups of individuals are spoken of under different specific -names. The cedars of Lebanon, known as _Cedrus libani_, occur as -isolated groups on the Lebanon hills as outliers of the larger -forests of the Taunus 250 miles distant. The African cedar, _Cedrus -atlantica_, is separated from the Lebanon cedar by a distance of 1400 -miles. Approximately the same distance divides the Lebanon cedar from -the deodar, _Cedrus deodara_, which extends from Afghanistan along -the Himalayas almost to the confines of Nepal. Sir Joseph Hooker -regards the three cedars as varieties of one species which once -formed a continuous forest: he attributes the present discontinuous -distribution, in part at least, to the effects of a warmer succeeding -a colder climate. The less favourable conditions drove the vegetation -of the lowlands to seek more congenial habitats at higher altitudes. -In this connexion it is interesting to find that in Algeria the cedar -is confined to the higher ground where the snow lies long in the -spring(21). - -The Tulip Tree of North America and Central China affords one of -many examples of existing flowering plants which illustrate the -close connexion between present distribution and past history. The -genus Liriodendron, often cultivated in the south of England, is -now represented by two species, the best known of which--the Tulip -Tree, _Liriodendron tulipera_--extends from Vermont to Florida and -westwards to Lake Michigan and Arkansas. The leaves bear a superficial -resemblance to those of the Sycamore, but are as a rule easily -distinguished by the truncated form of the apex; the specific name -was suggested by the tulip-like form of the flowers. Fossil leaves -of Liriodendron are not uncommon in the Cretaceous rocks of Disco -Island in latitude 70° N., where they occur with other flowering -plants which bear striking testimony to the mildness of the Cretaceous -climate in high northern latitudes. One of the associated flowering -plants is a species of Artocarpus, described by Dr Nathorst as -_Artocarpus Dicksoni_ which bears a close resemblance to _A. incisa_ -the bread-fruit tree of the southern tropics of the Old World. Without -attempting to deal fully with the past history of Liriodendron, it may -be confidently stated that the records of the rocks are consistent with -the idea of antiquity suggested by the present distribution of the two -surviving species. - -Islands such as Great Britain and Ireland, situated a short distance -from a continent, contain many plants which are widely spread in -different parts of the world, together with a very small number -peculiar to the British Isles though closely allied to species on the -neighbouring continent or to plants farther afield. The occasional -recognition of species previously believed to be confined to Britain -tends to reduce the short list of our endemic types. - -An enquiry into the origin of an island flora involves a consideration -of the data in regard to changes in level and relative distribution of -land and water in the course of geological evolution. It is generally -agreed that at no distant date, in a geological sense. Great Britain -and Ireland were united to the continent. There is, however, another -fact to reckon with, namely the prevalence of Arctic conditions in -northern Europe when a thick sheet of ice spread over the greater -part of the British Isles. There can be no doubt that the severity of -the climate during the Glacial period was such as to destroy a large -proportion of the vegetation. The question is, were all the flowering -plants destroyed or were some of the hardier species able to survive, -either on the higher peaks which kept their heads above the level of -the ice or on the southern fringe of England beyond the ice-covered -region? It is impossible to give a definite answer: the probability -is that nearly all the pre-Glacial species were destroyed, but it is -not impossible that some Alpine-Arctic plants escaped extinction, -while others retreated to more southern and less Arctic areas by means -of a land-connexion with France or crossed the intervening sea by -ocean-currents, by animal agency, or by wind. - -Although we possess but imperfect information as to the extent and -duration of land-bridges between Britain and the continent, there are -no special difficulties in the way of accounting for the presence -of Scandinavian, Germanic, and other elements in the British flora. -There are, however, other and more difficult problems to consider in -reference to a small group of flowering plants which are met with in -the west and south of Ireland, also, to a less extent, in Cornwall and -in a few other localities in the south-west of England. In Connemara -in the west of Ireland, where hard frosts are unknown and winter snows -are rare, there are three kinds of Heath, St Dabeoc's Heath (_Daboecia -polifolia_), the Mediterranean Heath (_Erica mediterranea_) and -_Erica Mackaii_ which are not found elsewhere in the British Isles or -in the whole of northern Europe, but reappear in the Pyrenees. The -London Pride (_Saxifraga umbrosa_), another Pyrenean plant, grows -on the south and west coast of Ireland from Waterford to Donegal. -_Arbutus Unedo_, the Strawberry tree, which flourishes in the Killarney -district of County Kerry and occurs in neighbouring localities, has -a wide distribution in the Mediterranean region. Devonshire and -Cornwall possess two other Heaths, _Erica ciliaris_, which extends into -Dorsetshire and occurs in north Brittany, and _Erica vagans_, both -Pyrenean species, while a Mediterranean plant. _Gladiolus illyricus_, -grows in the New Forest. - -In 1846 Edward Forbes dealt with the problems presented by the -distribution of British plants in an essay which has exercised a -far-reaching influence. When Forbes published his work, comparatively -little was known as to the possibilities of transport of seeds and -fruits across barriers of water(22). His conviction that the known -means of dispersal were insufficient to account for the presence of -Mediterranean or Lusitanian plants in Ireland led him to turn to -geology for a solution of the problem. He was thus led to put forward -the view that in the course of the Tertiary period when, as we know -from palaeontological evidence, the climate of north and west Europe -was much warmer than it is now, and long-before the beginning of the -climatic changes which culminated in the Glacial period, there was a -land-connexion between the west of Ireland and the south-west of the -continent. Mr Praeger, whose work on the Irish flora is well known to -systematic botanists, agrees with the conclusions of Forbes, and sees -in the Portuguese and Mediterranean plants 'relics of a vegetation -which once spread along a bygone European coast-line which stretched -unbroken from Ireland to Spain'(23). If this explanation is correct it -entitles Arbutus, St Dabeoc's heath and other members of this southern -group to be regarded as a very old section of our flora. There is, -however, another side to the question: granting that a certain number -of Irish plants were able to withstand the rigours of an Ice age, it -is hardly likely that the strawberry tree and other southern types, -which it is admitted flourish in the south-west of Ireland because of -the mildness of the climate, were of the number of those which endured -an extreme Arctic phase. Moreover, if these Mediterranean species -are survivals from the Tertiary period, if they have been isolated -since pre-Glacial days as an outlier of a southern flora, we might -fairly expect that during the long interval between their arrival and -the present day new forms would have been produced closely related -to, though not identical with, the parent types. This, however, -has not been proved to be the case. Darwin in speaking of Forbes' -Essay in a letter to de Candolle in 1863 says that he differs from -most of his contemporaries 'in thinking that the vast continental -extensions of Forbes, Heer, and others are not only advanced without -sufficient evidence, but are opposed to much weighty evidence'(12). -The alternative view is to regard Arbutus and its compatriots as -post-Glacial arrivals and not as survivals from a widely spread -Tertiary flora. - -A recently published account of the New Flora of the volcanic island -of Krakatau furnishes an instructive and remarkable demonstration of -the facility with which a completely sterilised island, separated -by several miles of ocean from neighbouring lands, may be restocked -with vegetation(24). In 1883 the island of Krakatau, then densely -covered with a luxuriant tropical vegetation, was partially destroyed -by a series of exceptionally violent volcanic explosions. After this -catastrophe only a third of the island was left: the surface was deeply -covered by pumice and volcanic ash and no vestige of life remained. In -1906 a party of botanists who spent a few hours on Krakatau collected -137 species of plants: the vegetation was in places so dense that it -was with the greatest difficulty they penetrated beyond the coastal -belt, and some of the trees had reached a height of 50 feet. The seeds -and fruits of this new flora have been carried by ocean-currents, -by wind, and by the agency of birds from other islands in the Malay -Archipelago. The nearest islands, except the small island of Sebesi, -about 12 miles distant, are Java and Sumatra, separated from Krakatau -by a stretch of water about 25 miles in breadth. It is reasonable to -wonder whether, had Forbes known of this and similar modern instances -of the capabilities of plants as travellers, he would have adopted the -view he did. In this connexion it may be added that in recent years the -glaciation of Ireland has been shown to be more extensive than it was -believed to be when Forbes wrote his essay. - -There would seem to be no insuperable objection to the conclusion -that the Mediterranean plants in Ireland and in the south of England -reached their present home after the retreat of the ice at the end -of the Glacial period, and after Ireland became an island. A full -consideration of the problem is beyond the scope of this book, but -I have briefly stated the case, not with the authority of an expert -but in order to draw attention to a particularly fascinating study in -plant-migration. - -[Illustration: Fig. 2. _Eriocaulon septangulare_ With. West Connemara. -(Photograph by Mr W. R. Welch.) ] - -In a volume by W. Canton entitled _A Child's book of Saints_ a story is -told in which the presence in Ireland of Mediterranean species receives -a more picturesque explanation. The Monk Bresal was sent to teach the -brethren in a Spanish monastery the music of Irish choirs. In later -years Bresal longed for a sight of his native land, though he loved his -home and 'every rock, tree, and flower' in his adopted country. After -returning to Ireland, his thoughts reverted to Spain; 'it appeared -to him as though he was once again in a granite nook among the rocks -beside the Priory'; he saw the ice-plant with its little stars of white -flowers sprinkled with red (the London Pride) and a small evergreen -tree from which he had often gathered the orange-scarlet berries -(Arbutus). The Prior of the Spanish monastery 'with heavenly vision -saw Bresal gazing at the evergreen tree and the ice-plant, and turning -to the trees blessed them and commended them to go and make real his -dream. As Bresal brushed away his tears he saw with amazement at his -feet the ice-plant and hard by the evergreen tree.' - -The plant represented in Fig. 2 is another British species which tasks -the ingenuity of students of plant-geography. This is the Pipe Wort -(_Eriocaulon septangulare_), the sole representative in Europe of a -certain family of Monocotyledons: it flourishes in the west of Ireland -and in the western islands of Scotland but nowhere else in Europe; it -is native on the other side of the Atlantic in Canada and the northern -United States of America. Mr Praeger in describing the striking mixture -of species in the west of Ireland writes, 'The pool from which we -gather the American Pipe Wort is fringed with Pyrenean Heathers. The -cracks which are filled with the delicate green foam of the maiden hair -are set in Bearberry and Spring Gentian; _Habenaria intacta_, far from -its Mediterranean home, sends up its flower-spikes through carpets of -mountain Avens; and St Dabeoc's Heath and the dwarf Juniper straggle -together over the rocky knolls'(25). - -The presence of Eriocaulon on the western edge of Europe may be -attributed to migration in pre-Glacial days from North America by way -of a land-connexion, of which Greenland and Iceland represent surviving -portions. The opinion held by Forbes, and advocated by some later -naturalists, that the southern companions of Eriocaulon in the west of -Ireland are survivors from a Tertiary flora which have lived through -the Ice Age, is consistently extended to the Pipe Wort. On the other -hand, before yielding to the temptation to regard these American and -Mediterranean species as links with the Tertiary period, we must be -convinced that the possibilities of post-Glacial introduction, even -without the aid of land-bridges, have been exhausted. The Pipe Wort is -a botanical puzzle which affords a good example of the accession of -interest to field-botany effected by a knowledge of the distribution -of the component members of the British flora. The problem of its past -history suggests an experimental enquiry into the adaptability of its -seeds to dispersal, and emphasises the importance of the co-operation -of botanists and geologists in a common endeavour to trace the origin -of British plants. - -In addition to the Pipe Wort, mention may be made of three other -American flowering plants recognised in the Irish flora. _Sisyrinchium -angustifolium_ recorded from the west of Ireland is native in temperate -North America; the orchid, _Spiranthes romanzoffiana_, met with in the -south and north of Ireland, is widely spread in Canada and the northern -States, while _Sisyrinchium californicum_, a native of California -and Oregon, was discovered by Mr Marshall in marshy meadow-land near -Wexford(26). In the case of the more recently discovered American -immigrants, the possibility of human introduction must be borne in -mind, though there are no special reasons for doubting that some, as in -the case of Eriocaulon, reached the Irish coast by natural agencies. - - - - -CHAPTER III - -THE GEOLOGICAL RECORD - - 'All the Epochs of the Past are only a few of the front carriages, - and probably the least wonderful, in the van of an interminable - procession.' - J. B. Bury (_The Science of History_). - - -The portion of the earth's surface accessible to investigation is made -up in part of accumulations of old sediments, some indistinguishable -from the shingle, sand, and mud now in process of formation by the -ceaseless action of denudation; others have been hardened, gently -folded or violently contorted and so far altered by crust-movements -as to render their sedimentary origin well nigh unrecognisable. It is -these sediments of former ages, the dust of lost continents, in which -are preserved the majority of the fragmentary remains of plants and -animals, the flotsam and jetsam of successive phases of evolution. - -The crust of the earth, as Darwin wrote, 'with its imbedded remains -must not be looked at as a well filled museum, but as a poor collection -made at hazard and at rare intervals'(19). It is from this imperfect -record that we seek to discover the relative antiquity of the several -groups or genera of living plants, and in the structure of extinct -types we endeavour to discover connecting links between divisions of -the plant kingdom which in the course of evolution have retained little -or no signs of a common descent. - -Sir Joseph Hooker in a letter to Darwin in 1859 speaks of his -'conviction that we have not in a fossilised condition a fraction of -the plants that have existed, and that not a fraction of those we have -are recognisable specifically'(12). Considering the nature of the -palaeontological documents the wonder is how much they have taught us, -and we may look with confidence to the results of future research in -a field of which the importance has only recently been appreciated. -With the strata of sedimentary origin are frequently associated igneous -rocks, and in many continental regions, as in the majority of oceanic -islands, the crust of the earth consists wholly of volcanic material or -of rocks produced by the gradual solidification of molten magmas. Rocks -composed mainly of carbonate of lime, such as limestones and chalk, -bear witness to ocean beds or to sediments deposited on the floors of -inland seas beyond the reach of land detritus where coral reefs were -reared or the shells and other calcareous skeletons of animals supplied -the material for future land. In such rocks the remains of calcareous -seaweeds are frequently recognisable and occasionally, as in the -English chalk, fragments of wood testify to transport from a distant -land. - -While there is little difficulty in explaining the nature of much of -the earth's crust, in several parts of the world the strata are totally -unfossiliferous and closely simulate crystalline rocks. In many cases -it is believed that such strata represent ancient sediments which in -the course of ages have been reduced by metamorphic agencies to a -condition which has obscured or entirely obliterated all traces of -their pristine state. - -Since the pioneer work of William Smith, who in the early days of the -nineteenth century first realised the importance of fossils as aids to -the determination of relative age, geologists have devoted themselves -to the task of correlating the sedimentary rocks of the world, using -as criteria the order of superposition of the strata and the nature of -their organic remains. The result has been to classify portions of the -earth's crust into periods or chapters, which together constitute a -record of geological evolution as complete as it is possible to obtain -from the available data. The accompanying table shows the order of -sequence of the epochs, which stand for terms of years of a magnitude -beyond our powers to grasp. - -The division of geological history into larger and smaller periods does -not imply the recurrence of sudden revolutions; it is in some measure -dictated by considerations of convenience, but more particularly by -our ignorance of certain stages in the history of the world due to the -imperfection of the record. - - -GEOLOGICAL TABLE. - -Showing the position in the Geological Series of the strata referred to -in this volume. - - Tertiary (Cainozoic) - - { =Recent= { Superficial accumulations containing human - { =Pleistocene= { remains (Metal age, Neolithic and - { { Palaeolithic ages, Glacial deposits) - { - { =Pliocene= Cromer Forest-bed, etc. - { - { =Miocene= Absent from Britain. - { - { =Oligocene= Bovey Tracey beds, etc. - { - { =Eocene= London Clay, etc. - - - Secondary (Mesozoic) - - { =Cretaceous= { Chalk - { { Wealden beds - { - { { Purbeck and Portland beds (Upper Jurassic) - { =Jurassic= { Oolites (Middle Jurassic) - { { Lias (Lower Jurassic) - { - { { Rhaetic beds - { =Triassic= { Keuper " (Marls with rock-salt, etc.) - { { Bunter " - - - Primary (Palaeozoic) - - { =Permian= { Red Sandstones, etc. - { { Magnesian limestone - { - { { Coal Measures - { =Carboniferous= { Millstone Grit - { { Carboniferous limestone - { - { =Devonian= { Devonian limestones, etc. - { { Old Red Sandstones - { - { =Silurian= { Sandstones, shales, - { { some limestone - { - { =Ordovician= { Slates, sandstones, - { { Volcanic rocks, etc. - { - { =Cambrian= { Slates, Sandstones, etc. - { - { =Pre-Cambrian= { Slates, Volcanic rocks, etc. - { =or Archean= - -In certain parts of the world, as for example the north-west Highlands -of Scotland, the Malvern Hills, Scandinavia, and in many other regions -in Europe and North America, geologists have recognised what they -believe to be the foundation stones of the world. These Archaean -rocks, which underlie the oldest fossiliferous strata, belong to a -period of geological evolution from which it appears to be hopeless to -obtain any light as to the nature of the contemporary organic world. -The earliest vestiges of life so far discovered exhibit a high degree -of organisation, which unmistakably points to their being links in a -chain extending far beyond the limits of the oldest Cambrian strata -in which recognisable fossils first occur. The rocks of the Cambrian -and Ordovician epochs, as represented by the grits, shales, slates and -other sedimentary strata in Wales, Shropshire, the Lake district and -elsewhere, though in places rich in the remains of animals, afford -no information in regard to the land vegetation. From the succeeding -Silurian epoch very little evidence has been gleaned as to the nature -of the flora, and it is not until we come to the sedimentary rocks of -the Devonian era that records of plant-life occur in any abundance. The -almost complete lack of botanical data in the pre-Devonian formations -is in part due to the fact that these older rocks consist to a large -extent of marine deposits formed under conditions unfavourable to the -preservation of plants. That the land-surfaces of the older Palaeozoic -eras supported an abundant vegetation there can be little doubt. -The relics of plant-life furnished by the Devonian and succeeding -formations represent the upper branching-systems of a deeply rooted and -spreading tree, the lowest portions of which have been destroyed or -have left no sign of their existence. - -In descending the Geological series, we begin with superficial -deposits, such as peat and river-gravels found subsequently to the -underlying boulder-clay of the Glacial period. The remains of forest -trees preserved in the peat and in submerged forests round the -coast connect the vegetation of the historic period with that of the -Neolithic age. At the base of the Pleistocene series, the name given -to the latest chapter of geological history, we find evidence of the -prevalence of arctic conditions in the widely spread boulder-clays and -other deposits of the Glacial period. - -From deposits of post-Glacial date abundant plant remains have -been obtained, but we cannot say with any degree of certainty what -proportion of these plants remained in Britain during the Ice age, -and whether the greater part of the vegetation, the relics of which -have been discovered in pre-Glacial beds, was destroyed or driven -south by the advancing ice. We may briefly consider some of the more -interesting facts brought to light by the investigation of the fossil -plants in the Lower Pleistocene and Upper Tertiary beds. It is mainly -to the researches of Mr Clement Reid into the vegetation of Britain -immediately preceding the Glacial period, that our knowledge of this -phase of the history of the British flora is due. - -[Illustration: Fig. 3. Pre-Glacial plants from Mundesley (A), Norfolk -and Pakefield (B, C), Suffolk. (Photographs by Mr Clement Reid and Mrs -E. M. Reid.) A. _Bidens tripartita_ Linn. (× 6); B. _Picea excelsa_ -Linn. (nat. size). C. _Stellaria holostea_ Linn. (× 12).] - -On the coast of Norfolk in the neighbourhood of Cromer the sections -of the cliffs reveal the existence of a succession of sands, clays, -and gravels underlying Glacial deposits; this material was probably -laid down near the mouth of the ancient Rhine, which in the latter -part of the Tertiary period flowed across a low area, which is now -occupied by the shallow southern half of the North Sea(27). The -plant-fragments found in these river-sediments indicate a temperate -climate. Among the plants of this pre-Glacial flora are many familiar -British species, such as _Caltha palustris_ (marsh marigold), species -of butter-cup, _Stellaria holostea_ (greater stichwort) (Fig. 3, C), -_Bidens tripartita_ (bur-marigold) (Fig. 3, A), maple, hawthorn, the -alder, hazel, the yew, Scots pine and numerous others. If, as is not -improbable, these pre-Glacial plants were swept away by the subsequent -arctic conditions, the great majority of them returned to their old -home when a warmer climate ensued. There are however some pre-Glacial -plants, such as the spruce fir (_Picea excelsa_), a cone of which -is shown in Fig. 3, B, the water chestnut, _Trapa natans_ (Fig. 4), -and a few other species no longer represented in the British flora. -The genus _Trapa_ is a striking example of a flowering plant which -has disappeared since the Tertiary period from many parts of Europe, -including England, most of Sweden, and from several regions in northern -Europe. It still grows in a few localities in Switzerland and in some -of the Italian lakes. In pre-Glacial times the water chestnut was -widely spread from Portugal and England in the west to Siberia in the -east, and its hard four-pronged nuts have been recorded from many -post-Glacial peat-moors in the north of Europe. - -[Illustration: Fig. 4. _Trapa natans_ Linn. (nat. size). From -Mundesley. (Photographs by Mr and Mrs Reid.)] - -From the so-called Cromer forest-bed and associated deposits on the -Norfolk coast several pre-Glacial plants have been obtained, indicating -a temperate climate during this phase of the Pleistocene period. A few -arctic species, such as the dwarf birch and arctic willow obtained from -the deposits next above the Cromer forest-bed, herald the near approach -of glacial conditions. - -It may be remarked in passing that no satisfactory evidence has been -discovered in Britain of the existence of man in this part of Europe in -pre-Glacial days: it is, however, believed that flints from Tertiary -strata on the continent show traces of human workmanship. As Sir -Edwin Ray Lankester said in 1905, 'It is not improbable that it was in -the remote period known as the Lower Miocene--remote as compared with -the gravels in which Eoliths [primitive stone implements] occur--that -Natural Selection began to favour that increase in the size of the -brain of a large and not very powerful semi-erect ape'(28). - -Though comparatively recent in terms of geological chronology, the -remoteness, according to ordinary conceptions of time, of the Tertiary -period is brought home to us when we endeavour to grasp the fact -that it was during this chapter in the earth's history that some of -our highest mountain-ranges, such as the Alps, the Carpathians, and -Himalayas were formed by the uplifting of piles of marine sediments. -From Tertiary strata in the Isle of Wight, on the Hampshire coast, and -in the London basin numerous fossil plants have been obtained, which -afford convincing evidence of climatic conditions much more genial than -those of the present day. The presence of palm leaves and of a wealth -of other sub-tropical plants in Lower Tertiary beds in England reveals -the existence of a flora differing considerably both from that in the -uppermost Tertiary beds of Norfolk and from the modern British flora, -but closely allied to the present Mediterranean flora. - -The basaltic columns of the Giants' Causeway and of the Staffa Cave, -and the terraced rocks which form so characteristic a feature in the -contours of the Inner Hebrides, are portions of lava-flows, which in -the early days of the Tertiary period were poured out over a wide area -of land stretching from the north-east of Ireland, through the Western -isles of Scotland, the Faroë islands, to Iceland and Greenland. While -in this northern region volcanic activity was being manifested on a -stupendous scale, a shallow sea extended over part of what is now the -south-east of England in which was deposited a considerable thickness -of sedimentary material derived from the neighbouring land. In this -upraised sea-floor, known as the London clay, which is exposed in the -Isle of Sheppey and in many other localities, numerous fossil fruits -and fragments of wood occur in association with marine shells. The -fact that many of the fruits were ripe at the time of their entombment -led some eighteenth century writers to assign an autumn date to the -universal deluge. One of the Sheppey fruits may be mentioned as an -especially interesting sample of the early Tertiary flora, namely -the genus Nipadites, so named from the very close resemblance of the -fossils to the fruits of the existing tropical plant Nipa. _Nipa -fruticans_, sometimes described as a stemless palm because of the -absence of the erect stem which is usually a characteristic feature of -palms, grows in brackish estuaries of many tropical countries (Fig. -5, A): it has long leaves not unlike those of the date-palm and bears -clusters of fruits as large as a man's head; a single fruit is two or -three inches long and its hard fibrous shell is characterised by four -or five longitudinal ribs (Fig. 5, B). The fruits of Nipa, which may be -carried a considerable distance by ocean-currents without losing the -power of germination, are constantly found with other vegetable drift -on the beaches of tropical islands. The discovery of fruits of Nipa (or -Nipadites), hardly distinguishable from those of the existing species, -in Tertiary beds in England, Belgium, in the Paris basin, and in Egypt -affords a striking instance of changes in the geographical distribution -of an ancient plant now restricted to warmer regions. - -[Illustration: Fig. 5. _Nipa fruticans_, Thunb. A. On the coast of the -Malay Peninsula. (Photograph by Prof. Yapp.) B. Head of fruits (1/5 -nat. size). From a specimen in the British Museum.] - -While the higher members of the Cretaceous system, as seen in the chalk -cliffs and downs, represent the upraised calcareous accumulations on -the floor of a fairly deep and clear sea, the lower members testify to -shallower water within reach of river-borne sand and mud. 'During the -Chalk period,' as Huxley wrote, 'not one of the present great physical -features of the globe was in existence. Our great mountain ranges, -Pyrenees, Alps, Himalayas, Andes, have all been upheaved since the -chalk was deposited, and the Cretaceous sea flowed over the sites of -Sinai and Ararat'(29). - -The Wealden strata, at the base of the Cretaceous system, as seen on -the Sussex coast, in parts of the Isle of Wight, in the Weald district -of Kent and neighbouring counties, point to the existence of a lake -over a portion of the south of England and of the English Channel. The -remains of a rich Wealden flora have been collected from these Wealden -sediments, notably from the plant-beds of Ecclesbourne near Hastings, -in which, so far as we know, flowering plants played no part or at most -occupied a very subordinate position. A few fossil leaves have been -described from rocks assigned to a Wealden age,--and from the older -Stonesfield Slate, of Jurassic age, a single leaf is recorded,--which -seem to be those of Dicotyledons; but it is certain that even in the -early days of the Cretaceous period the present dominant group in -the plant kingdom was in its infancy and in many regions probably -unrepresented. When we glance at the geological table and consider -that in all the floras from the Wealden down to the Devonian period, -flowering plants played no part, we are able to appreciate the fact of -their rapid development, referred to in a previous chapter, when once -this highest type had become established. - -The rocks comprised in the Jurassic system extend from East Yorkshire -to the coast of Dorsetshire; they consist of a succession of -limestones, clays, sandstones, and a few thin beds of impure coal. -Sediments of this age also occur, though to a much less extent, on -the north-east coast of Scotland and in a few places in the Inner -Hebrides. Many of the Jurassic strata contain only marine shells, -and corals are occasionally abundant, though in the lower members of -the system in the cliffs near Lyme Regis and at Whitby fossil plants -are fairly common. It is, however, from the middle Jurassic beds, -in the cliffs between Whitby and Scarborough, and in some inland -quarries in East Yorkshire, that we have obtained the richest Jurassic -flora. Rivers from a northern land laden with sediment and carrying -drift-wood, leaves and other plant fragments, deposited their burden in -an estuary which occupied the eastern edge of Yorkshire. Sedimentary -rocks laid down towards the close of the Jurassic period in the island -of Portland in the south and on the Sutherland coast in the north have -furnished valuable records of plant-life. - -The passage from the Jurassic to the underlying Triassic system is -formed by some shales and limestones in South Wales containing remains -of fish and other marine organisms. These so-called Rhaetic beds are -poorly represented in the British area, but on the continent of Europe -and in other regions the sediments of this age bulk much more largely -and have yielded a rich collection of plants. The rocks of the upper -division of the Triassic system, as seen in the Midlands, point to -the prevalence of desert conditions; and in the grooved sand-polished -surfaces of granite in Charnwood forest we have a glimpse of a -Triassic landscape. The salt-bearing strata of this period in Cheshire -and Worcestershire suggest conditions paralleled at the present day -in the Caspian and Dead-Sea regions. The vegetation of Britain, and -indeed of the world as a whole, seems to have undergone but little -change during the enormous lapse of time represented by the sediments -comprised between the Wealden and Triassic periods. The Lower Triassic -flora affords evidence of a change in the facies of the vegetation and -prepares us for the still greater differences revealed by a study of -the Permian and Carboniferous floras. To the student of evolution these -Palaeozoic floras are of special interest on account of the facts they -have contributed in regard to the descent and inter-relationship of -different branches of the vegetable kingdom. - -It is by a patient study of the waifs and strays of the vegetation -of successive phases of the world's history preserved in sedimentary -strata, that it has been possible to follow the history of many -existing plants and to establish links between the present and the -past. - - - - -CHAPTER IV - -PRESERVATION OF PLANTS AS FOSSILS - - 'Some whim of Nature locked them fast in stone for us afterthoughts - of Creation.' - Lowell. - - -The failure of the earlier naturalists to grasp the true significance -of fossils or even to appreciate their nature is an extraordinary fact -when we consider the pioneer work which they accomplished in biological -and geological science. The following extract from the writings of so -enlightened a man as John Ray serves to illustrate an almost incredible -disinclination to admit what seems to us the obvious. He wrote:--'Yet -I must not dissemble that there is a Phenomenon in Nature, which doth -somewhat puzzle us to reconcile with the prudence observable in all its -work, and seems strongly to prove, that Nature doth sometimes _ludere_, -and delineates figures, for no other end, but for the ornament of some -stone, and to entertain or gratify our curiosity, and exercise our -wits. This is, those elegant impressions of leaves and plants upon -cole-slate, the knowledge of which, I must confess myself to leave to -my learned and ingenious friend Mr Edward Lhwyd of Oxford.... He told -me that Mr Woodward, a Londoner, shewed him very good draughts of the -common female fern, naturally formed in cole.... But these figures are -more diligently to be observed and considered... Dr Woodward will have -them to be the impressions of the leaves of plants which were there -lodged at the time of the Deluge'(31). - -The Mr Woodward alluded to by Ray thus expressed his views on fossils -in an _Essay towards the Natural History of the Earth_:--'The whole -terrestrial globe was taken all to pieces and dissolved at the Deluge, -the particles of stone, marble, and all solid fossils dissevered, taken -up into the water, and then sustained together with sea shells and -other animal and vegetable bodies; the present earth consists and was -formed out of that promiscuous mass of sand, earth, shells, and the -rest falling down again, and subsiding from the water'(32). - -In the later part of the seventeenth-century Steno, a Dane by birth and -Professor of Anatomy at Padua, by his recognition of the identity of -the teeth in a shark's head, which he had dissected, with some fossils -from Malta known as Glossopetrae, established the true nature of -fossils. He also recognised a certain orderly sequence in fossiliferous -strata, and in the opinion of Professor Sollas he is entitled to be -considered the 'Father and Founder' of Geology(33). - -It was by slow degrees that the early observers freed themselves from -the obsession that the remains of animals and plants in the earth's -crust bear witness to a Universal Deluge and are all identical with -existing species. The possibility that some of the fossil plants in -English strata might be more clearly related to forms now met with in -warmer regions was gradually realised. The publication of the _Origin -of Species_ stimulated palaeontological research, and botanists as well -as zoologists turned to the investigation of extinct genera in search -of proofs of the doctrine of evolution. - -The common occurrence of petrified wood in rocks of different ages -is well known. Fossil stems are occasionally found in their natural -position of growth, the structural details being rendered permanent by -the deposition of siliceous or calcareous material from water drawn by -capillarity into the dead but still sound tissues. Petrified wood from -Upper Jurassic beds is abundant in the Island of Purbeck; an unusually -long piece of stem may be seen in the small town of Portland fixed -to the wall of a house. Some of these stems have been referred by an -American author to the Araucarian family of Conifers, but the structure -is as a rule hardly well enough preserved to afford satisfactory -evidence for identification. In his _Testimony of the Rocks_, Hugh -Miller speaks of fossil wood from the upper beds of the Jurassic system -in sufficient abundance on the beach at Helmsdale in Sutherlandshire to -be collected in cart-loads; it is still easy to pick up good specimens -on the shingle beach a short distance north of Helmsdale, and a recent -microscopical examination showed that some specimens are pieces of an -Araucarian tree. - -Impressive examples of petrified trees on a large scale are to be -seen in the United States, in Arizona and the Yellowstone Park. -(Frontispiece.) In the northern part of Arizona the country for over -an area of 10 square miles is covered with tree trunks, some reaching -200 feet in length and a diameter of 10 feet. The nature of the -mineralising substance has given rise to the name Chalcedony Park for -this Triassic forest(34). A striking example of one of the Arizona -trees is exhibited in the British Museum and in a neighbouring case is -a splendid petrified stem, 9 ft. in height, of a conifer discovered in -Tertiary lavas in Tasmania(35). - -[Illustration: Fig. 6. Section of the north face of Amethyst Mountain, -Yellowstone Park, including upwards of 2000 ft. of strata. The -steepness of the slope is exaggerated. (After W. H. Holmes.)] - -Figure 6 illustrates the preservation of a series of forests of -Tertiary age in the mass of volcanic sediments, 2000 feet in thickness, -known as Amethyst mountain, in the Yellowstone Park district. By the -weathering away of the surrounding volcanic material the tall stems of -the trees are exposed in places on the mountain sides like the 'columns -of a ruined temple.' The height of the river at the foot of the cliff -is 6700 ft. above sea-level and the mountain rises to a height of -9400 ft. above the sea. In the lower part of the section the volcanic -strata are seen to rest on a foundation of older rocks _A_, and these -in turn were laid down on the eroded surface of a still more ancient -foundation, _B_(36). - -The section as a whole affords a striking demonstration of the -magnitude of earth-movements since the last of these forests was -buried below the surface of a sea in which the volcanic material -was deposited. The account of the Yellowstone Park section recalls -Darwin's description in the _Naturalist's Voyage_(37) of snow-white -columns projecting from a bare slope, at an altitude of 7000 ft. in the -Cordillera. - -The abundance of drift-wood on the coasts of some countries at the -present day helps us to picture the conditions under which the remains -of former forests have been preserved. In his _Letters from High -Latitudes_, Lord Dufferin gives the following description of drift-wood -on the shores of Spitzbergen:--'A little to the northward, I observed, -lying on the sea-shore innumerable logs of drift-wood. This wood is -floated all the way from America by the Gulf Stream, and as I walked -from one huge bole to another, I could not help wondering in what -primeval forest each had grown, what chance had originally cast them on -the waters, and piloted them to this desert shore'(38). A photograph -reproduced in Amundsen's book on _The North West Passage_ shows the -beach on the Alaskan coast strewn with drifted timber(39). For the -accompanying photograph (Fig. 7) of the flood-plain of the Colorado -River(40), I am indebted to Professor MacDougal of the Desert Research -Laboratory at Tucson, Arizona, who in a recent letter writes, 'During -times of high-water a thin sheet of flood covers the flat for many -miles and bears drift-wood so thickly that it is difficult to push a -boat through it.' The drift-wood consists of poplar, willow, pine, and -juniper, 'the last two have been brought from the upper river, from -as far away as a thousand miles.' A picture such as this affords an -admirable example of the wealth of material available for preservation -in a fossil state. - -It is only in the minority of cases that the accidents of preservation -of fragments of ancient floras have given us the means of investigating -the internal structure of the plant organs. It is far more frequently -the case that fossil plants are represented only by a carbonised film -on the surface of a piece of shale or other rock: the actual substance -of the plant has been converted into a thin layer of coal, and though -the venation and other surface-features may be clearly revealed, the -internal tissues have been destroyed. If a lump of clay containing a -piece of fern frond is heated, the result is an impression of the leaf -on the hardened matrix and a coaly substance in place of the plant -substance. It is occasionally possible by detaching a piece of the -black film from a fossil, and heating it with nitric acid and chlorate -of potash and then dipping it in ammonia, to obtain a transparent -preparation suitable for microscopical examination of the cell-outlines -of the superficial layer of the leaf or other plant-fragment. This -method of examination, used by several students of fossil plants and -with conspicuous success by Professor Nathorst of Stockholm, often -affords valuable aids to identification. - -[Illustration: Fig. 7. Flood-plain of the delta of Rio Colorado. The -hills in the background are 25 miles distant. (From a photograph by -Prof. MacDougal.)] - -Pieces of plants embedded in sandy sediment, if not preserved by -petrifaction, that is by the introduction into the tissues of some -siliceous or calcareous solution, gradually decay and their fragmentary -remains may be washed away by percolating water, leaving a hollow mould -in the gradually hardening sediment, which is afterwards filled with -sand or other material. The plant itself is destroyed, but a cast is -taken which in the case of fine-grained sediments reproduces the form -and surface-pattern of the original specimen. The incrustation of -plants by the falsely named petrifying springs of Knaresborough and -other places illustrate another method of fossilisation. - -[Illustration: Fig. 8. Flower of _Cinnamomum prototypum_ Conw. -preserved in amber. × 10. (After Conwentz.)] - -Plants which owe their preservation to amber occur both as -incrustations and petrifactions. This fossil resin occurs in Tertiary, -Cretaceous, and Jurassic rocks; the amber found in abundance on the -Baltic coast near Danzig and occasionally picked up on the beach -in Norfolk and Suffolk comes from beds of Tertiary age. Pieces of -Pine-wood have been described from the Baltic beds in which the tissues -are perfectly preserved as the result of the conversion into amber -of the resinous secretion which permeates their cells: in this case -the amber is a petrifying agent. More frequently the preservation is -due to incrustation; as resin trickled down the stems of the Tertiary -pines from an open wound, flowers and leaves, blown by the wind on to -the sticky surface, were eventually sealed up in a translucent case -of amber. Though the actual substance may have gone, the mould which -remains exhibits in wonderful perfection each separate organ of a -flower or the delicate hair-clusters on the surface of a leaf. The -flower represented in Fig. 8, a species of Cinnamon, is one of several -specimens described by the authors of a monograph of Tertiary plants in -the Baltic amber(41). - -The fragments of plants preserved in nodules of calcareous rock -occasionally met with in some of the Lancashire and Yorkshire -coal-seams are perhaps the most striking examples of the possibilities -of petrifaction. By cutting sections of these nodules and grinding them -to a transparent thinness, the most delicate tissues of Carboniferous -plants are rendered accessible to investigation under the high power of -a microscope. As our attention is absorbed by the examination of the -details of cell-structure it is easy to forget that the section has not -been cut from a living plant, but from the twig of a tree which grew in -the forests of the Coal age. The preservation is such as to enable us -not only to describe the anatomy of these extinct types of vegetation, -but, by the application of the knowledge of the relation between the -structure of the plant-machine and its functions gained by a study of -living species, it is possible in some degree to picture the plants -of the Coal period as living organisms and to see in the structural -framework a reflection of external environment. The recognition in the -general architectural plan of the Palaeozoic plants, as in many of the -finer anatomical features, of the closest resemblance to plants of -the modern world produces an almost overwhelming sense of continuity -between the past and the present. - -The plants of the Palaeozoic period, though often differing -considerably from those of the same class in the floras of to-day, -exhibit a remarkably high type of organisation. Some of the most -abundant trees in the forest of the Coal age are decidedly superior in -the complexity of their structure, as also in size, to modern survivals -of the same stock. On the other hand, it must be remembered that -Monocotyledons and Dicotyledons which now occupy the highest place in -the hierarchy of plants have left no sign of their existence in any -of the Palaeozoic strata. The greater size of some of the Palaeozoic -plants, and in some respects the more advanced stage of evolution which -they represent as compared with their nearest relatives of the present -era, must be considered in relation to their more important and -relatively higher position in the plant-world than that which is now -held by their diminutive descendants. It is, however, impossible to get -away from the conclusion that the oldest Palaeozoic flora of which we -have an intimate knowledge must be the product of development of an age -which is represented by a chapter in the history of the plant kingdom -at least as far removed from the beginning as it is separated from the -chapter now being written. Examples might be quoted in illustration of -the risks attending the determination of fossils by means of external -features alone, but it may suffice to mention the case of a specimen -originally described as a fragment of a Cretaceous Dinosaur under the -name _Aachenosaurus multidens_. By the examination of thin sections -this supposed bone was shown to be a piece of Dicotyledonous wood(42). -The methods of preservation of plants as fossils are numerous and -varied and the few examples selected give but an incomplete idea of the -subject: for a fuller treatment of fossilisation the reader is referred -to more technical treatises (48 vol. I.). - -The employment of fossil plants as 'Thermometers of the ages' is a -branch of Palaeobotany to which a passing allusion may be permitted -though it is only indirectly connected with the main question. As -one of the most interesting examples of changed climatic conditions -revealed by a study of fossil plants, reference may be made to the -wealth of material collected within the Arctic circle. The problems -suggested by the discovery of plants in rocks of various ages in -North Siberia, Spitzbergen, Franz Josef Land, Bear Island, Greenland, -and in many other localities in the far north are too difficult and -far-reaching to be discussed in these pages. In the Cretaceous and -Tertiary strata of the west coast of Greenland and Disco Island from -69° to 72° north latitude, to refer only to one case, a great number of -plants have been obtained by several of the earlier Arctic explorers -and more recently by members of one of the Peary Expeditions. At the -present day on the fringe of land on the western edge of Greenland -which is not permanently covered with ice, a considerable number of -herbaceous plants are able to exist and to produce seed during their -concentrated period of development; while trees are represented only -by a few low-growing shrubs such as the dwarf Juniper. In places -accessible to investigation beyond the ice-covered hills of northern -Greenland the rocks have been shown to consist of Cretaceous and -Tertiary sediments containing fossil plants associated with seams -of coal. From these beds numerous Dicotyledons have been obtained, -some of them almost identical with living species characteristic of -sub-tropical or tropical countries. In the lowest of the Cretaceous -series no Dicotyledons have been found, but flowering plants are -abundant in the higher Cretaceous rocks. Allowing for the fact that -closely allied species are often able to live under very different -climatic conditions, there can be no doubt that the Cretaceous -and Tertiary floras of Greenland indicate an average temperature -considerably higher than that which now prevails in the warmest parts -of the British Isles. - -In the far south a fairly rich Jurassic flora has recently been -discovered by the members of a Swedish Antarctic expedition in Graham's -Land in latitude 63°·15 S. and longitude 57° W., which in its general -facies bears a close resemblance to the Jurassic flora of Yorkshire. - -Although the great majority of the records of ancient plants are -difficult to interpret by reason of imperfect preservation and because -of the frequent separation of leaves, stems, and reproductive organs, -the student who tries to piece together the _disjecta membra_ of the -floras of the past shares the opinion expressed by the late Marquis of -Saporta,--'Si l'on s'attache à les déchiffrer, on oublie bien vite la -singularité des caractères, et le mauvais état des pages. La pensée se -lève, les ideés se développent, le manuscrit se déroule; c'est la tombe -qui parle et livre son secret.' - - - - -CHAPTER V - -FERNS; THEIR DISTRIBUTION AND ANTIQUITY - - 'It has been shown that certain forms persist with very little - change, from the oldest to the newest fossiliferous formations; and - thus show that progressive development is a contingent, and not - a necessary, result of the nature of living matter.' - Huxley. - - -The Ferns as a whole represent a section of the vegetable kingdom -which traces its ancestry as far into the past as any group of plants. -Impressions of leaves on the shales of the Coal-measures and on rocks -of the earlier Devonian period are hardly distinguishable in form and -in the venation and shape of the leaflets from the finely divided -fronds of modern ferns. Until a few years ago these Palaeozoic fossils -were generally regarded as true ferns, and it was believed that ferns -played a conspicuous part in the vegetation of the earliest periods, of -which we have any botanical knowledge. Conclusions based on external -form must frequently be revised in the light of more trustworthy -evidence. It was shown in the later part of the nineteenth century by -the late Professor Williamson of Manchester, whose researches into -the plants of the Coal age shed a flood of light on the ancestry -and inter-relationship of many existing plants, that some of the -fern-like leaves which have long been familiar to those who search -among the shales of the refuse heaps of collieries, were borne on -stems differing in anatomical features from those of any known fern. -The investigation of the structure of the leaves and their supporting -stems led to the recognition of certain extinct genera of Palaeozoic -plants of exceptional interest, to which the term generalised type is -aptly applied. Associated with anatomical and other characters such -as we now regard as the attributes of ferns, these plants exhibit -other features not met with in modern ferns but characteristic of a -group of seed-bearing plants known as the Cycads. Recent research has -revealed the existence of several such generalised types which, by -their combination of characters now met with in distinct sub-divisions -of the plant-kingdom, clearly indicate the derivation of Ferns, and -Cycads as we know them to-day, from a common stock. It was in the -first instance by means of anatomical evidence--obtained by the -microscopical examination of sections of petrified fragments of stems -and leaves--that the generalised nature of these Palaeozoic plants was -recognised. Nothing was known as to the reproductive organs. Ferns as -now represented in the floras of the world are essentially seed-less -plants. As the author of _Hudibras_ wrote: - - 'Who would believe what strange bugbears - Mankind creates itself, of fears? - That spring like fern, that insect weed, - Equivocally, without seed.' - -The reproductive organs or spores borne on the fronds of a fern -produce, on germination, a thin green structure, known as the -prothallus, less than an inch in length: this bears the sexual organs, -and as the result of the union of the male and female cells, the embryo -fern-plant begins its existence as a parasite on the inconspicuous -prothallus, until after unfolding its first green leaf and thrusting a -slender root into the ground, it starts its career as an independent -organism[2]. In this life-cycle the seed plays no part. - -[2] The life-history of a Fern is clearly described by Prof. Bower in a -recent volume in this series. - -It is noteworthy that the absence of any indication of spore-capsules -and spores, in the case of some of the supposed fern leaves from -the Coal-measures, caused some suspicion in the mind of an Austrian -Palaeobotanist as to the right of such specimens to be classed among -the ferns. This opinion, based in the first place on negative evidence -and but little regarded by other authors, has in recent years been -proved correct. In 1904 a paper was read before the Royal Society -by Professor Oliver and Dr Scott(43) in which evidence was brought -forward pointing to the conclusion that one of these generalised plants -bore true seeds. Subsequently Dr Kidston published an account of some -specimens of another of these Palaeozoic plants in which was actually -shown an organic connexion between undoubted seeds and pieces of a -fern-like frond(44). Without entering into further details, these and -similar discoveries may be summarised as follows:--Many of the supposed -Fern-fronds of Palaeozoic age, particularly those characteristic of -the Coal-measures, are the leaves of plants which in their anatomical -characters combined features now shared by true Ferns and by the -Cycads. The reproductive organs of these Palaeozoic genera differed -widely from those of existing ferns; the male organs, while not unlike -the spore-capsules and spores of certain ferns, recall the male organs -of living Conifers and Cycads, and the female organs were represented -by seeds of a highly complex form. These seed-bearing plants have -been called Pteridosperms, a name which expresses the combination -of fern-like features with one of the distinguishing attributes of -the higher plants, namely the possession of seeds. The ancestors of -Pteridosperms are as yet unknown; it is, however, reasonable to assume -that there existed in some pre-Carboniferous epoch a group of simple -plants from which both Ferns and Pteridosperms were derived. In the -forests of the Coal age true Ferns probably occupied a subordinate -position in relation to the Pteridosperms. - -The question of the relationship between different families of recent -ferns and the older known fossil members of the group is beyond the -scope of this book. Evidence has been discovered in recent years which -warrants the statement that, although none of those Carboniferous ferns -were generically identical with existing forms, they very clearly -foreshadowed some of those structural features which characterise more -than one family of present-day Ferns. The records of the older Mesozoic -formations afford abundant evidence of the existence of certain types -of Ferns showing a very close resemblance to recent species. - -[Illustration: Fig. 9. _Osmunda regalis_ Linn. Fertile frond, (2/5 nat. -size.)] - -An enquiry into the geographical distribution of living Ferns reveals -facts of special interest in connexion with the relative antiquity of -different genera and families. The wide distribution of the Bracken -fern has already been referred to: it is abundant in Tasmania; its -vigour in the island is well illustrated by Mr Geoffrey Smith's -statement that constant attention is necessary to keep it from invading -newly opened country(45). On Mount Ophir in the Malay Peninsula the -cosmopolitan bracken occurs in association with the two genera Matonia -and Dipteris, ferns which are among the most striking examples of links -with a remote past and have a restricted geographical range. With -_Osmunda regalis_, the Royal Fern, the Bracken is conspicuous in the -marsh vegetation of the Bermudas; it flourishes on the Atlas Mountains, -in the Canary Islands, in Abyssinia, on Mt Kenia, in British East -Africa, in the Himalayas, and is in fact generally distributed in the -tropics in both the north and south temperate zones. - -The Royal Fern (Fig. 9) is another British species with a wide -distribution; it occurs in Northern Asia and in North America; it is -common in the Siberian forests and lives in several tropical countries, -extending to Southern India and Cape Colony, and in South America it -is represented by a closely allied species. Though at the present day -_Osmunda regalis_ is one of the rare English Ferns, its occurrence in -the submerged forest-beds round our coasts and in pre-Glacial beds -points to its former abundance in the British area generally. The Royal -Fern is a member of a family now represented by two genera, Osmunda and -Todea. - -With the exception of _Todea barbara_, with its large spreading -fronds and a short root-covered stem, which occurs in Australia and -Cape Colony, all the species of this genus are filmy ferns with -semitransparent fronds adapted to a moisture-laden atmosphere. The -maximum development of the genus is in New Zealand. - -_Todea barbara_ affords an instance of discontinuous distribution; it -was no doubt once widely spread in circumpolar regions and now survives -only in South Africa and in Australia. - -There are satisfactory reasons for regarding the Bracken Fern, with -its world-wide range in present-day floras, as a comparatively modern -species now in full vigour. Its anatomical and other features are -consistent with the view that it is a late product of evolution, and -as yet no indication has been given by the records of the rocks of an -ancient lineage. The Osmunda family, on the other hand, is undoubtedly -an extremely old branch of the fern group. A comparison of the Royal -Fern with the Bracken shows that their stems are constructed on -very different plans, and we have good reasons for speaking of the -structural peculiarities of the former as those of a more primitive -type. Moreover, the discontinuous geographical range of some members of -the Osmunda family is in itself an indication of antiquity. There is -another point which may have a bearing in this question of antiquity, -namely the fact that the spores of Osmunda are green and do not possess -the powers of indurance inherent in the spores of the majority of -ferns which are not green. It has recently been contended by Professor -Campbell of Stanford University that the delicate green spores of the -Liverworts, plants closely allied to the Mosses, constitute an argument -in favour of the antiquity of these plants(46). Certain Liverworts are -cosmopolitan in their range, _e.g._ the genera Riccia and Marchantia. - -If certain genera are widely distributed, notwithstanding the fact -that their reproductive cells, by which dispersal is effected, are -ill-adapted to withstand unfavourable conditions or to endure prolonged -desiccation, it would seem reasonable to conclude that their emigration -has been accomplished slowly and with difficulty. Ferns such as -Osmunda, with green and short-lived spores, would thus be handicapped -in competition with other genera provided with more efficient means of -dispersal and better equipped for the vicissitudes of travel. - -The inferences as to antiquity deduced from a study of the existing -species of Osmunda and Todea receive striking confirmation from the -testimony of fossils. Some of the oldest known Palaeozoic ferns, -though differing too widely from the existing Osmundas and Todeas -to be included in the same family, afford distinct glimmerings of -Osmundaceous characters, which at a later period became individualised -in the direct ancestors of the modern forms. Our knowledge of the -past history of the Osmunda family has recently been considerably -extended and placed on a firmer basis by the researches of Dr Kidston -and Professor Gwynne-Vaughan. These authors have recognised in some -exceptionally well-preserved fern-stems from Permian rocks in Russia, -anatomical features which point unmistakably to close relationship with -the recent members of the family(47)(48). - -Passing higher up the geological series, fertile fern fronds with -spore-capsules and spores practically identical with those of Osmunda -have been found in the Jurassic plant-beds of Yorkshire and in rocks of -approximately the same age in many parts of the world. From Jurassic -strata in New Zealand a petrified fern-stem has been described -(_Osmundites Dunlopi_), almost identical in structure with the -surviving species. Cretaceous and Tertiary examples of similar ferns -might be quoted; but enough has been said to establish the claim of the -Royal Fern and other members of the Osmunda-family to an ancestry which -possibly extends even farther back than that of any other existing -family of Ferns. - -[Illustration: Fig. 10. _Gleichenia dicarpa_ Br. (1/2 nat. size.)] - -A brief reference may be made to another fern now represented by -several species widely disseminated in tropical and sub-tropical -countries. The genus Gleichenia occurs abundantly in the warmer regions -of both the Old and New World. The fronds may usually be recognised -by their habit of growth (Fig. 10); in several species the main axis -is repeatedly forked and a small bud between the divergent branches -of the forks forms a characteristic feature. The leaflets are either -long and narrow like the teeth of a comb or short and bluntly rounded. -Moreover the anatomy of the creeping stem affords a ready means of -identification. We have satisfactory evidence of the occurrence of -Gleichenia in European floras during both the Jurassic and Cretaceous -periods. Numerous fragments of plants were obtained some years ago, -not far from Brussels, from the Wealden strata in which the famous -skeletons of Iguanodon were discovered. Visitors to the Natural -History Museum in Brussels are no doubt familiar with the skeletons of -this enormous herbivorous animal: in the same gallery are exhibited -the remains of the fossil plants from the Iguanodon beds. Some of -these fragments are pieces of fern fronds identical in form with -those of existing Gleichenias. The microscopical examination of some -exceptionally well preserved fragments of Wealden stems discovered by -Prof. Bommer of Brussels enabled him to recognise the Gleichenia type -of structure and thus to confirm the inconclusive evidence furnished -by fragmentary leaves. The most interesting records in regard to the -former occurrence of Gleichenia in Northern Europe we owe to the late -Oswald Heer of Zurich, who has described many examples of Gleichenia -fronds from rocks of Lower Cretaceous age in Disco Island on the west -coast of Greenland in latitude 70° N. The same type of fern is recorded -also from upper Jurassic beds in the north-east of Scotland, in the -Wealden rocks of Sussex, as well as from other European localities. It -is clear that the Gleichenia-family, no longer represented in north -temperate floras, was in the Jurassic period, and especially in the -early days of the Cretaceous period, widely spread in Europe, extending -well within the Arctic circle. It may be that the original home of -Gleichenia was in the far North at a time when climatic conditions were -very different from those which now prevail. Gleichenia, like many -other northern plants, retreated to more southern regions where, in -the warmer countries of the world, many species still flourish widely -separated in space and time from the place of their birth. - -The ferns so far mentioned have a more or less extended distribution -at the present day. In the case of _Pteridium aquilinum_, the -cosmopolitan Bracken Fern, wide range would seem to be correlated -with comparatively recent origin; on the other hand, the facts of -palaeobotany show that the wide distribution of Osmunda, a type of fern -which differs in many important respects from members of the family -(Polypodiaceae) to which the Bracken belongs, is not inconsistent -with an exceptionally ancient family-history. There are, however, -certain genera of ferns which afford remarkable examples of restricted -geographical distribution associated with great antiquity. The island -of Juan Fernandez, 420 miles off the coast of Chili, the home for -four years of Alexander Selkirk (to whose adventures we owe Defoe's -creation of Robinson Crusoe), is interesting also from a botanical -point of view. The vegetation of this oceanic island, 20 square miles -in area with basaltic cliffs rising to a height of 3000 ft. above the -sea, includes more than 40 species of ferns, eight of which occur -nowhere else. One of these endemic ferns is _Thyrsopteris elegans_, the -only representative of the genus; it is readily distinguished by its -large and graceful fertile fronds, examples of which may occasionally -be seen on a plant of this species in the Royal Gardens at Kew: the -sporangia are produced in circular cups which replace the ordinary -leaflets on the lower branches of the frond and hang from the short -axis like miniature clusters of grapes. It is noteworthy that among -the fragmentary remains of the fern vegetation of the Jurassic flora -in England and in other parts of Europe specimens occur with fertile -segments practically identical with those of the Juan Fernandez -species. Students of fossil plants are occasionally led away by the -temptation to identify imperfect specimens with rare existing species -to which they exhibit a superficial resemblance, and this is well -illustrated by the frequent use of the generic name Thyrsopteris for -Jurassic and Lower Cretaceous ferns which are too imperfect to be -determined with any degree of certainty We have, however, satisfactory -grounds for the assertion that the Juan Fernandez fern affords a -striking confirmation of the truth of Darwin's dictum that 'Rarity, -as geology tells us, is the precursor to extinction.' In this remote -oceanic island, for reasons which we cannot explain, there lingers an -isolated type which belongs to another age. - -The following passage, which forms a fitting introduction to an account -of two other genera of ancient ferns, is taken from a description of -an ascent of Mount Ophir in the Malay Peninsula by Dr A. R. Wallace -in his well-known book on the Malay Archipelago:--'After passing a -little tangled jungle and swampy thickets, we emerged into a fine -lofty forest.... We ascended steadily up a moderate slope for several -miles, having a deep ravine on the left. We then had a level plateau or -shoulder to cross, after which the ascent was steeper and the forest -denser till we came out upon the Padang-Batu, or stone-field.... We -found it to be a steep slope of even rock, extending along the mountain -side farther than we could see. Parts of it were quite bare, but where -it was cracked and fissured there grew a most luxuriant vegetation, -among which the pitcher plants were the most remarkable.... A few -coniferae of the genus Dacrydium here first appeared, and in the -thickets, just above the rocky surface, we walked through groves of -those splendid ferns, _Dipteris Horsfieldii_ and _Matonia pectinata_, -which bear large spreading fronds on slender stems, 6 or 8 feet -high'(49). - -[Illustration: Fig. 11. _Matonia pectinata._ A group of plants in a -wood on Gunong Tundok, Mount Ophir. (Photograph by Mr A. G. Tansley.)] - -The two genera Matonia and Dipteris afford exceptionally striking -examples of survivals from the past. Matonia is represented by two -species, _Matonia pectinata_ (Fig. 11), which grows abundantly on the -upper slopes of Padang-Batu in dense thickets on the rock faces where, -as Mr Tansley states, its associates are a species of Gleichenia, -Dipteris, and a little _Pteridium aquilinum_ (Bracken Fern). _Matonia -pectinata_ occurs also on Bornean mountains at an altitude of over -3000 ft. and descends to the coast on some of the Malay islands. The -other species of the genus, _Matonia sarmentosa_, has so far been -found in one locality only, Niak, Sarawak, where it was discovered by -Mr Charles Hose. _Matonia pectinata_ has a creeping stem covered with -a thick felt of brown hairs bearing tall fan-shaped fronds divided -into numerous comb-like branches thickly set with narrow linear -leaflets on which circular clusters of spore-capsules are sparsely -scattered. In some respects Matonia is unlike other ferns; the fronds -constitute a striking feature, and the anatomy of the stem is still -more distinctive. In the form, development, and arrangement of the -sporangia (spore-capsules)--organs which from the constancy of their -characters have long been recognised as the most useful basis for -classification--Matonia exhibits distinctive features. - -In order to emphasise the isolated position of the genus it has -recently been placed in a separate family, the Matonineae, of which -it is the sole living representative. The restricted geographical -range of Matonia, considered in connexion with the clearly marked -peculiarities in structure and form, leads us to expect other evidence -in support of the natural inference that the genus is a survivor of -a once more vigorous and widely spread family. If Matonia were a -recently evolved type which has not spread far from its original home, -we should expect it to conform more closely than it does to other -ferns in the Malay region. Even assuming for the sake of argument -that variation may occur _per saltum_, and new forms may be produced -differing in more than the finer shades of small variation from their -parents, the peculiar features of Matonia are too pronounced and its -individual characteristics too obvious to warrant the assumption of -recent production. It is, however, from the testimony of the rocks that -we obtain confirmation of the opinion that these Malayan species are -plants on the verge of extinction. In shales of Jurassic age exposed -on the Yorkshire coast at Gristhorpe Bay and in iron-stained rocks of -the same age between Whitby and Scarborough, well preserved leaves have -been found agreeing in the shape of the frond, as also in the form of -the leaflets and of the groups of sporangia which they bare, with those -of _Matonia pectinata_. - -The exposure by a stroke of the hammer, on the fractured surface of -a rock picked up on the beach at Hayburn Wyke (a few miles south of -Whitby), of a piece of fern frond which is unmistakably closely allied -to the species described by Wallace on Mount Ophir, establishes a link -between the Jurassic and the present era and presents a fascinating -problem in geographical distribution. These fossil Matonias are known -to students of ancient plants as species of the genus Matonidium, a -name adopted by a German botanist for specimens apparently identical -with those from the Yorkshire coast discovered in slightly younger -rocks (Wealden) in North Germany. The same type has been found also in -sediments of Wealden age on the Sussex coast. Other leaf-impressions -agreeing closely with those of Matonidium have been obtained from -the Yorkshire Jurassic rocks and these are assigned to another genus -Laccopteris, an extinct member of the family Matonineae. It is not -merely in the habit of the fronds and in the shape and venation of the -leaflets that these fossil ferns resemble the existing species, but -the more important features exhibited by the spore-capsules supply -additional evidence. It has already been pointed out that the stems -of Matonia are characterised by a type of structure unknown in an -identical form in any other recent fern. - -A few years ago Prof. Bommer discovered fragments of leaves and -stems in Wealden beds a few miles from Brussels sufficiently well -preserved to reveal the details of internal organisation. Some of -these fossils were found to possess structural features identical -with those of the Malayan species of Matonia. A full account of the -fossil representatives of the Matonia family would be out of place in -a general essay on Links with the Past, but brief reference may be -made to some of the data which throw light on the geological history -of the family. In strata classed by geologists as Rhaetic, a phase -of earth-history between the Triassic and Jurassic eras (see p. 42), -species of Laccopteris and allied forms have been described from -several other countries; from Jurassic and Wealden strata examples of -both Laccopteris and Matonia have been found in Germany, Portugal, -Belgium, Austria, and elsewhere. From rocks of Cretaceous age, higher -in the series than the Wealden strata, well preserved impressions of a -Matonidium have been discovered in Moravia. The Matonineae were widely -distributed in Europe during the Rhaetic and Jurassic periods, but, so -far as we know, the family did not survive in the northern hemisphere -beyond the limits of the Cretaceous period. It is noteworthy that, in -spite of the preservation of the remains of Jurassic and Cretaceous -floras in many extra-European regions, notably in India, South Africa, -Australia, China, and Tonkin, no specimens have been found which can -with confidence be assigned to the Matonineae. A single fossil has, -however, been described from Queensland which may be a piece of a -Laccopteris frond. - -There is some evidence that ferns very similar to Matonia existed -in North America during the Mesozoic period. It would be in the -highest degree rash to assume that the Matonineae played no part in -the Jurassic vegetation of India, South Africa, and other southern -lands, but there can be little doubt that the family was especially -characteristic of European floras during a portion of the Mesozoic era. -It would seem that subsequent to the Wealden period the ancestors of -Matonia dwindled in numbers and their geographical range became much -more restricted. - -The records of Tertiary rocks have hitherto added nothing to our -knowledge of the distribution of the family subsequent to the -Cretaceous period. All we can say is that the existing species of -Matonia are the last survivors of a family which in the Jurassic period -overspread a wide area in Europe and probably extended to the other -side of the Atlantic. Exposed to unfavourable climatic conditions and -possibly affected by the revolution in the plant world consequent -on the appearance of the Flowering Plants, the Matonineae gradually -retreated beyond the equator until the two surviving species found a -last retreat in the Malayan region. - -[Illustration: Fig. 12. _Dipteris conjugata_ Rein. and, in the middle -of the upper part of the photograph, a frond of _Matonia pectinata_ R. -Brown. Mount Ophir. (Photograph by Mr A. G. Tansley.)] - -The fern spoken of by Dr Wallace as _Dipteris Horsfieldii_ (perhaps -better known as _Dipteris conjugata_ (Fig. 12)), which grows with -_Matonia pectinata_ on Mount Ophir and in the Malay region generally, -is one of seven species of a genus characterised by a somewhat wider -geographical range than Matonia. _Dipteris conjugata_ extends to the -Philippines, Samoa, Fiji, New Caledonia, New Guinea and Central China; -its fronds, like those of Matonia, are borne on long slender stalks -attached to a creeping stem; they have a broad lamina divided by a deep -median sinus into two symmetrical halves and each half is cut up into -segments with a saw-like edge. Several stout ribs spread through the -lamina from the apex of the long stalk like the open fingers of a hand; -from these ribs smaller veins are given off at a wide angle, and these -in turn give rise to a reticulum of finer veins forming a skeletal -system like that in the leaves of an oak and many other flowering -plants. - -Numerous groups of spore-capsules are borne on the lower surface of -the broad lobed frond. The leaves of other species of Dipteris have -the same type of structure, but in some the segmentation of the lamina -is carried further and the leaf consists of numerous long and narrow -segments with one or two main ribs. Dipteris is represented in the -flora of Assam, and it is interesting to find that a species recently -discovered in Borneo is more closely connected with the Assam type -than with those of the Malay region. Until a few years ago the genus -Dipteris was included in the large family Polypodiaceae of which -nearly all our British ferns are members, but the discovery of certain -distinguishing features in the structure of the sporangia showed that -these Eastern and Southern species form a fairly well-defined group -worthy of family rank. - -In the Rhaetic plant-beds of Northern and Central Europe, of North -America, Tonkin, and elsewhere, numerous fossil leaves have been -discovered which in shape, venation, and in the manner of occurrence of -the sporangia bear a close resemblance to species of Dipteris. Ferns -of this type were abundant in the Jurassic floras of the northern -hemisphere, and it is interesting to find impressions of Dipteris-like -leaves both in the Jurassic rocks of the Yorkshire coast as well as in -slightly newer beds of the same geological period on the north-east -coast of Sutherland. - -It is impossible to say with confidence how nearly these Rhaetic and -Jurassic ferns were related to the existing species, as our knowledge -of them is less complete than in the case of the fossil representatives -of the Matonineae, but there can be no reasonable doubt that in -Dipteris as in Matonia we have a connecting link between the present -and a remote past. - - - - -CHAPTER VI - -THE REDWOOD AND MAMMOTH TREES OF CALIFORNIA - - 'Your sense is sealed, or you should hear them tell - The tale of their dim life, with all - Its compost of experience....' - W. E. Henley. - - -Since their introduction into England about the middle of the -nineteenth century, the two Californian species _Sequoia sempervirens_ -(the Redwood) and _Sequoia gigantea_ (the Mammoth tree) have become -familiar as cultivated trees. The name Sequoia, said to be taken -from Sequoiah, the inventor of the Cherokee alphabet, was instituted -in 1847, while the name Wellingtonia, often used in horticulture -though discarded by botanists in favour of the older designation -Sequoia, was proposed in 1853. Both species are now confined to a -comparatively small area in California: their restricted geographical -range, considered as an isolated fact, might be regarded as a sign of -recent origin. The records of the rocks, however, afford ample proof -that rarity in this as in many other instances is the precursor of -extinction. The famous groves of Mariposa and Calaveras represent the -last resting-place of giant survivors of a race which formerly held its -own in Europe and in other parts of the world. - -The Redwood, _Sequoia sempervirens_, occupies a narrow belt of country, -rarely more than 20 or 30 miles from the coast, three hundred miles -long from Monterey in the south to the frontiers of Oregon; it has -a stronger hold on existence than Sequoia gigantea. In Northern -California it still forms pure forests on the sides of ravines and on -the banks of streams. The tapering trunk, rising from a broad base to -over 300 ft., gives off short horizontal branches thickly set with -narrow spirally disposed leaves 1/4-1/2 inch in length arranged in -two ranks like the similar leaves of the Yew. The lower edge of each -leaf is decurrent, that is it runs a short distance down the axis of -the branch instead of terminating at the point of attachment. It is by -paying attention to such details as this as well as to more important -features, that we are able to connect fragmentary fossil twigs with -those of existing species. The female 'flowers' have the form of oblong -cones from 3/4 to 1 inch long: each consists of a central axis bearing -crowded wedge-shaped, woody appendages or cone-scales, which gradually -increase in breadth towards the exposed distal end characterised by its -four sloping sides and by a median transverse groove. Several small -seeds are borne on the upper surface of the cone-scales. The smaller -and short-lived male flowers need not be described. - -[Illustration: Fig. 13, _Sequoia gigantea._ King's Co., California. -(From Prof. D. H. Campbell)] - -The other and better known species _Sequoia gigantea_ (Fig. 13) has an -even more restricted range and is confined to groves on the western -slopes of the Sierra Nevada between 3000 to 9000 ft. above sea-level. - -This tree is at once distinguished from the Redwood by its ovate, -sharply pointed and stiffer leaves which retain their spiral -disposition and closely surround the axis of the twigs like -obliquely-set needles. The cones are of the same type as those of -_Sequoia sempervirens_, but are broader and may attain a length of -3-1/2 inches (9·5 cm.) (Fig. 14). - -Reference has already been made to Sequoia as a striking illustration -of longevity. It is also selected as an equally impressive example of -a type verging on extinction, which played a prominent part in the -vegetation of both west and east during the Cretaceous and Tertiary -periods. - -[Illustration: Fig. 14. _Sequoia gigantea_ Torr. (7/8 nat. size.)] - -Scraps of branches with leaves hardly distinguishable from those of -the existing Californian trees are frequently met with in Tertiary -and Mesozoic sediments, and with them occasionally occur cones too -imperfectly preserved to afford satisfactory evidence of more than -superficial agreement with those of the recent species. The task of -deciphering the past history of plants, particularly of the Conifers, -is accompanied by many difficulties and insidious temptations. It is -clear from a critical examination of many of the recorded instances -of fossil Sequoias that the generic name has been frequently used -by writers without adequate grounds. The fragmentary specimens -available to the botanical historian cannot as a rule be subjected -to microscopical investigation, and even a partial acquaintance with -the similarity of the foliage of different types of living Conifers -is sufficient to convince the student of the need of self-control in -the identification of the fossils. It is, however, easy to point out -obvious pitfalls, though difficult to maintain a judicial attitude in -the excitement of endeavouring to interpret documents which are too -incomplete to be identified with certainty. If we put on one side all -records of supposed fossil Sequoias not based on satisfactory data, -there remains a wealth of material testifying to the antiquity of the -surviving species. - -It is by no means improbable that Conifers closely allied to the -Redwoods and Mammoth trees of California were represented in Jurassic -floras; but hitherto no proof has been obtained of the occurrence of -a Sequoia among the rich material afforded by the Jurassic plant-beds -of Yorkshire and by beds of the same age in other countries. A small -cone has recently been described from strata near Boulogne belonging -to the latest phase of the Jurassic period, which presents a strong -resemblance in shape and size and in the form of the cone-scales to -those of the recent species. This specimen, though not conclusive, -is the most satisfactory indication of a Jurassic Sequoia so far -discovered. From Lower Jurassic rocks in Madagascar similar cones -have been recorded in association with foliage-shoots like those of -_Sequoia gigantea_, but here too the evidence is not beyond suspicion. -In plant-bearing strata of Wealden age, such as are exposed in the -cliff near Hastings and in deposits of the same age in North Germany, -Portugal, and elsewhere, twigs and cones have been found which may be -those of trees nearly allied to the genus Sequoia. - -[Illustration: Fig. 15. _Sequoia Couttsiae_ Heer. Twigs (A) and -cone-scales (B) from Bovey Tracey. (× 3.) (Photographs by Mr and Mrs -Clement Reid.)] - -It is, however, in the sedimentary rocks of Cretaceous age, rather -higher in the series than those in the Hastings cliffs, and in the -succeeding Tertiary rocks, that undoubted Sequoias are met with in -abundance. At Bovey Tracey in Devonshire there is a basin-shaped -depression in the granitic rocks of Dartmoor filled with clay, gravel -and sand--the flood-deposits of a Tertiary lake containing waifs -and strays of the vegetation on the surrounding hills. Among the -commonest plants is one to which the late Oswald Heer gave the name -_Sequoia Couttsiae_, and his reference of the specimens to the genus -Sequoia has been confirmed by the recent researches of Air and Mrs -Clement Reid(50). This Tertiary (Oligocene) species is represented by -slender twigs almost identical with those of _Sequoia gigantea_ and by -well-preserved cone-scales and seeds (Fig. 15). Moreover, it has been -possible to examine microscopically the structure of the carbonised -outer skin of the leaves and to demonstrate its agreement with that -of the superficial tissue in the leaves of the Mammoth tree. With the -Bovey Tracey Sequoia are associated fragments of Magnolia, Vitis, and -_Taxodium distichum_, the swamp Cypress of North America, together -with other types which have long ceased to exist in Western Europe. -Other British examples of Sequoia have been described from Tertiary -beds at Bournemouth, the Isle of Wight, Sheppey, and Antrim, but the -material from these localities is inferior in preservation and cannot -be identified with the same degree of certainty as in the case of the -Devonshire specimens. The occurrence of twigs and cones of several -species of Sequoia in both Cretaceous and Tertiary rocks in Austria, -Germany, Italy, France, and elsewhere, shows that the ancestors of the -Californian trees were common in the European region. - -The exploration of Cretaceous and Tertiary rocks in Arctic Europe -has revealed the former existence in Greenland, Spitzbergen, and -other more or less ice-covered lands of plants which clearly denote -a mild climate. Cones and branches of Sequoias have been found in -abundance in Lower Tertiary beds on Disco Island off the west coast -of Greenland, and similar evidence of the northern extension of the -genus has been obtained from Spitzbergen. Dr Nathorst of Stockholm -speaks of twigs of Sequoia in the Tertiary clays of Ellesmere Land -almost as perfect as herbarium specimens. In Tertiary beds on the banks -of the Mackenzie River, in Alaska, Saghalien Island and Vancouver -Island, and in Upper Cretaceous rocks in the Queen Charlotte Islands, -remains of Sequoia have been discovered. One of the most remarkable -instances of the preservation of trees of a bygone age is supplied -by the volcanic deposits of Lower Tertiary age exposed on the slopes -of Amethyst mountain in the Yellowstone Park district. At different -levels in the volcanic and sedimentary material, which is piled up to -a height of over 2000 ft. above the valley, as many as fifteen forests -are represented by erect and prostrate limbs of petrified trees (Fig. -6). The microscopical examination of some of these trees has shown -that they bear a striking resemblance to _Sequoia sempervirens_. In a -photograph of these petrified forests by the U.S. Geological Survey -(36, 2) one sees living Conifers side by side with the lichen-covered -and weathered trunks of the fossil species (_Sequoia magnifica_), -living and extinct being at a distance hardly distinguishable. -(Frontispiece.) - -In concluding this brief survey of the fossil records of Sequoia, -reference may be made to the discovery of petrified wood in Cretaceous -rocks in South Nevada, possessing the anatomical features of _Sequoia -gigantea_, which shows that close to the present home of the big trees -their ancestors flourished during a period of the earth's history too -remote to be measured by human reckoning. - -The distribution of the Tertiary and Cretaceous Sequoias would appear -to have been mainly in the northern hemisphere, extending well within -the Arctic circle. It is, however, by no means improbable that the -ancestors of Sequoia flourished far south of the equator. Reference has -been made to Jurassic fossils from Madagascar which have been compared -with the existing species, and from Lower Tertiary beds in New Zealand -the late Baron Ettingshausen described some cones and twigs as _Sequoia -novae zeelandicae_ which bear a close resemblance to the existing -type. The available evidence would seem to point to a northern origin -of the genus, though allowance must be made for erroneous conclusions -based on negative evidence. Further research may well extend the past -distribution of Sequoia in southern lands, but the data to hand point -to the conclusion that the Californian trees represent the survivors -of a type which flourished in the Cretaceous and Tertiary periods over -a wide area in North America and in what we now call the Continent of -Europe. - - - - -CHAPTER VII - -THE ARAUCARIA FAMILY - - 'And so the grandeur of the Forest-tree - Comes not by casting in a formal mould, - But from its own divine vitality.' - Wordsworth. - -As an additional illustration of existing cone-bearing trees which form -links with the past we may briefly consider the genera Araucaria and -Agathis, the two members of the family Araucarieae. It is generally -agreed that the branches of the genealogical tree of this family -extended farther back into the past than in the case of the majority -of Conifers. By some authors the surviving representatives of the -Araucarian stock are considered to have a strong claim to be regarded -as the most primitive as well as the oldest of cone-bearing trees, -though this opinion, like many others, is not held by botanists as -a whole. This is not the place to discuss matters of controversy, -and I shall confine myself to a general consideration of Araucaria -and Agathis from the point of view of their present distribution -and the part they played in the vegetation of the Mesozoic and -Tertiary epochs. In 1741 a plant from Amboyna, one of the Moluccas, -was described under the name _Dammara alba_. For this tree, known -as the Amboyna Fine, the English botanist Salisbury instituted the -generic name Agathis, from a Greek word (αγαθις) meaning a ball of -string and probably suggested by the form of the cones, which is the -designation usually adopted in botanical literature instead of the -pre-Linnean term Dammara. The best known species of the genus is the -Kauri Pine, probably the finest forest tree in New Zealand where it -still flourishes from the North Cape to latitude 38° S., though the -occurrence of sub-fossil trunks and pieces of buried resin shows that -the Kauri forests are gradually dwindling. The stems of this species, -_Agathis australis_, rise like massive grey columns to a height of 160 -ft., terminating in a succession of spreading branches given off in -tiers from the main trunk. The thick narrow lanceolate leaves, with -several parallel veins, reach a length of 2 to 3 inches. The female -shoots have the form of small and almost spherical cones consisting of -a central axis bearing overlapping spiral series of broadly triangular -scales (Fig. 16). Each scale carries a single seed with a large -wing attached to one side which facilitates disposal by wind. Other -species of Agathis occur in the Malay Archipelago, the Philippines, -in Queensland, in the New Hebrides, New Caledonia, the Fiji Islands, -and elsewhere. With the exception of the Australian Kauri (_Agathis -robusta_), with leaves larger and broader than those of the New Zealand -Kauri, the genus is essentially an island type. With the exception of -some species of the southern hemisphere genus Podocarpus, there are no -Conifers with foliage like that of Agathis. It is, however, the broad -and thin single-seeded scales and the spherical cones, in some species -six inches in length, which furnish the most trustworthy means of -identifying the genus. - -[Illustration: Fig. 16. A. _Agathis robusta_ Muell. (much reduced). B. -_Agathis Moorei_ Lind. (1/2 nat. size).] - -[Illustration: Fig. 17. _Araucaria excelsa._ The upper part of a small -tree in the Cambridge Botanic Garden. (Much reduced.)] - -The allied genus Araucaria, with the exception of two South American -species, the familiar Monkey Puzzle, _Araucaria imbricata_, and -a Brazilian tree, _Araucaria brasiliana_, is confined within the -geographical area occupied by Agathis. The name Araucaria was first -used by de Jussieu in 1789 for a plant previously referred to the -genus Pinus and described as one of the most beautiful trees of Chili. -This species, _A. imbricata_, introduced into England in 1796, grows -on the southern slopes of the Andes and, as in the case of the Kauri -forests of New Zealand, buried stems point to a wider extension of -the forests in earlier days. The sharp and thick leaves of the Monkey -Puzzle distinguish it from all other Conifers; its large almost -spherical seed-bearing cones, more than half a foot in length, which -may occasionally be seen on well-grown British trees, are unlike those -of other genera. Each of the deep and narrow scales bears a single -seed embedded in the substance of the scale and terminates distally -in a narrow upturned process. Some species of Araucaria, differing -considerably in the form of the leaves and in the shape and structure -of the seed-scales from the Chilian species, are conveniently placed -in a distinct sub-division of the genus Araucaria. Of this type the -Norfolk Island Pine, _Araucaria excelsa_, is the best-known example -(Fig. 17). It was introduced to Kew by Sir Joseph Banks in 1793, soon -after its discovery by Captain Cook, who describes the stems of the -Norfolk Island trees as resembling basaltic columns, and relates how on -approaching the island everyone was satisfied that the columnar objects -were trees, 'except our Philosophers, who still maintained they were -basaltes.' The leaves are short, about half an inch long, laterally -compressed and slightly spreading and sickle-shaped--sometimes shorter -and broader and overlapping--arranged in crowded spirals. The scales -of the broadly oval cones are single-seeded, but differ from those -of _Araucaria imbricata_ in having the seed exposed on the surface -and in the greater breadth and thinner borders of the scales. In both -Araucaria and Agathis the nature of the seed-scales constitutes a -distinguishing feature. The leaves of _Araucaria imbricata_ differ in -form from those of other Conifers. The foliage shoots of _Araucaria -excelsa_ and other species, _e.g._ the very closely allied _A. Cookii_ -of the New Hebrides and New Caledonia, though not unlike the branches -of a Japanese Conifer (_Cryptomeria japonica_), often cultivated in -England, afford fairly trustworthy characters for identification -purposes. - -The minute structure of the wood of both Araucaria and Agathis -constitutes an important distinguishing feature and enables us to -recognise on microscopical examination even a fragment of wood of -either of these genera. The small elongated cells or water-conducting -elements of the wood of the Araucarieae are characterised by one or -two, and occasionally as many as three or four, contiguous rows -of pits on their radial walls, and these appear in surface view as -flattened circles or polygonal areas. - -These details have been mentioned in order to show that Araucaria and -Agathis are sufficiently distinct in many respects from other Conifers -to render their identification in a fossil state comparatively easy, at -least much easier than the recognition of the majority of the members -of the Coniferae. It would be going too far to state definitely that -Araucarieae, as defined by reference to existing species, existed -during the Palaeozoic period; on the other hand it would seem in a -high degree probable that the vegetation of the Coal age and of the -succeeding Permian period included trees in which certain Araucarian -characters were clearly foreshadowed. The name Araucarioxylon was -formerly applied to petrified wood, obtained from Palaeozoic as well -as from later formations, which agrees anatomically with that of -Araucaria and Agathis. It has been shown in recent years that much of -the Palaeozoic wood of this type of structure belongs to the extinct -genus Cordaites, a tree which played a prominent part in the earlier -floras. Cordaites affords a good example of a generalised type: in its -wood-structure it resembles very closely the existing Araucarieae; -its long strap-like leaves are not unlike those of some species of -Agathis; its male flowers have often been compared with those of the -Maiden Hair tree, _Ginkgo biloba_, and certain anatomical features form -connecting links between this Palaeozoic genus and the Cycads. - -It is noteworthy that in another Palaeozoic genus, Walchia, the -leaf-bearing branches are identical in appearance with those of the -Norfolk Island Pine (Fig. 17) and some other species of Araucaria. -Unfortunately our knowledge of the reproductive organs of Walchia is -insufficient to warrant any definite statement as to the degree of -consanguinity between this Permian and Upper Carboniferous plant and -the Araucarieae; it is probable that in Walchia we have a type not far -removed from the line of evolution which led to Araucaria. Petrified -wood, identified as that of Walchia, and exhibiting the Araucarian type -of structure, has been recorded from Permian rocks of the Vosges. Other -instances might be quoted in support of the view that the Palaeozoic -floras included a few plants with which the surviving Araucarieae may -fairly claim relationship. Professor Zeiller of Paris has recently -described some fossil shoots from Palaeozoic rocks in India under the -name _Araucarites Oldhami_ on the ground of the similarity of the -leaves to those of _Araucaria imbricata_. Similarly, from Triassic -rocks several fossils have been described as closely allied to -Araucaria, in some cases because of anatomical resemblances and in -others on the less satisfactory evidence furnished by a similarity in -the foliage shoots. Professor Jeffrey of Harvard has recently given an -account of a new type of stem (Woodworthia) from the petrified Triassic -forest of Arizona possessing some Araucarian characters, though -differing from existing species of Araucaria in certain structural -features, a combination of characters regarded by this Author as an -indication of relationship with the family of Conifers, which includes -the Pines, Firs, Larches and other well-known northern genera. - -It is, however, from the records of Jurassic rocks that we obtain -the most satisfactory information as to the great antiquity and the -very wide geographical range of the ancestors of the recent genus. -The plant-beds of the Yorkshire coast afford clear evidence of the -occurrence of Araucarian trees in the woodlands of the Jurassic -period. Petrified wood has been found at Whitby, associated with jet, -showing the minute structural characteristics of the surviving species -of Araucarieae, and it is not improbable that some at least of the -Whitby jet has been formed from the wood of Araucarian plants. The -carbonised remains of leafy shoots preserved in the Jurassic shales -near Scarborough and on other parts of the Yorkshire coast include -twigs hardly distinguishable from those of _Araucaria excelsa_, though -the resemblance of external form alone, especially in the case of -foliage shoots, does not amount to proof of generic identity. We have, -however, the much more trustworthy evidence of cones and seed-bearing -scales in which the characteristic features of living species are -clearly shown. Seed-bearing scales almost identical with those of -_Araucaria excelsa_ and other recent species have long been known from -the Jurassic rocks of Yorkshire. - -From other parts of England where samples of Jurassic floras are -preserved, as at Stonesfield in Oxfordshire, in Northamptonshire and -elsewhere, equally striking examples of undoubted Araucarias have been -found. - -Fig. 18 represents part of a large cone described in 1866 by Mr -Carruthers from Jurassic rocks at Bruton in Somersetshire: this -specimen, now in the British Museum, consists of one side of a -spherical cone about 5 inches long and 5 inches broad; in size, as in -the form of the seed-scales, it shows a striking likeness to the cones -of the Australian species _Araucaria Bidwillii_, the Bunya Bunya of -Queensland. Other equally convincing examples of Jurassic Araucarian -cones and seeds may be seen in the museums of York and Northampton. On -the north-east coast of Sutherland there is a narrow strip of Jurassic -beds forming a low platform between the granitic and Old Red Sandstone -hills and the sea. From these rocks Hugh Miller described several -fossil plants in his _Testimony of the Rocks_, and an examination of a -large collection obtained from this district by the late Dr Marcus Gunn -shows that Miller was justified in speaking of Araucaria as a member of -this northern flora. - -[Illustration: Fig. 18. _Araucarites sphaerocarpus_ Carr. From Jurassic -rocks at Bruton, Somersetshire. (British Museum, 2/3 nat. size.)] - -There is abundant evidence pointing to the existence in Britain during -the Jurassic period, and in the early days of the Cretaceous epoch, of -Araucarian trees which differed but slightly from the modern species -confined to the southern hemisphere. In several localities in France, -Germany, and other parts of the continent, Araucarian fossils have -been recognised in Jurassic rocks. It is almost certain that some -foliage shoots and imperfectly preserved cones described by Dr Nathorst -from Upper Jurassic rocks in Spitzbergen were borne by a species of -Araucaria. Cone-scales very similar to those from Yorkshire have been -discovered in Wealden beds in Cape Colony, and Araucarian wood of -Jurassic and Cretaceous age has been found in Madagascar. From Jurassic -strata in India and Victoria (Australia), as well as from Upper -Jurassic and Lower Cretaceous rocks in Virginia and elsewhere in the -eastern United States, well preserved Araucarian fossils are recorded. -In a collection of Jurassic plants, obtained a few years ago by the -members of a Swedish Antarctic Expedition in Graham's Land, Dr Nathorst -has recognised some cone-scales of Araucaria, which demonstrate a -former extension of the family beyond the southern limits of South -America. - -It is interesting to find that when we ascend higher in the -geological series and pass beyond the Wealden strata to the Middle -and Upper sub-divisions of the Cretaceous period, evidence of the -wide geographical distribution of the Araucarieae is still abundant. -Araucarian wood has been obtained in rocks classed as Upper Cretaceous -in Egypt, in East Africa, in Dakota, and elsewhere. In the sedimentary -rocks of the Tertiary period undoubted examples of Araucaria are less -common, though there can be no doubt that the genus was much more -widely spread then than it is at the present day. The well-known -Tertiary plant-beds of Bournemouth have afforded specimens of foliage -shoots which have been described as a species of Araucaria, though in -the absence of well-preserved cones or petrified wood we must admit -that the data are inconclusive. It is, however, legitimate to regard -the striking similarity of the Bournemouth twigs to those of _Araucaria -excelsa_ and _A. Cookii_ as constituting a fairly strong case in -favour of the persistence of Araucaria in Western Europe up to the -earlier stage of the Tertiary period. Araucarian wood of Tertiary age -is recorded from India, while branches with broad leaves like those -of _Araucaria imbricata_ have been found in Seymour Island and the -Magellan Straits, and specimens of Tertiary wood are described from -Patagonia. At the other end of the world. Tertiary rocks on the west -coast of Greenland have yielded fragments which may be referred with -some hesitation to the genus Araucaria. - -A few words must be added in regard to the recent discovery by -Professor Jeffrey and Dr Hollick of some very interesting Cretaceous -specimens in New Jersey of well-preserved cone-scales and foliage -shoots of extinct plants closely related to the existing species of -Agathis(51). The American fossils are particularly valuable because -their preservation admits of microscopical examination of the tissues. -In Cretaceous rocks of Staten Island and in other localities on the -eastern border of the northern United States, kite-shaped seed-bearing -scales almost identical in form with those of recent species of Agathis -are fairly common fossils. Similar specimens have long been known -from Tertiary rocks in western Greenland. In the case of some of the -American examples each scale bore three seeds instead of a single seed -in living species: on account of this difference Prof. Jeffrey and Dr -Hollick have adopted a distinct generic name, _Protodammara_. - -The foregoing sketch is necessarily far from complete, but it may serve -as an illustration of the light which is thrown on the past history of -recent plants by the investigation of the relics of ancient floras. -The family Araucarieae now represented by a small number of species -which, with the exception of the Andian and Brazilian Araucarias, are -restricted to a small region in the southern hemisphere, was one of -the most widely spread sections of the seed-bearing plants during the -Mesozoic era. Ancestors of Araucaria must have been common trees in the -European vegetation in Jurassic and Lower Cretaceous periods, and even -as late as the Tertiary period there is evidence that representatives -of the family still lingered in the north. One conclusion which seems -almost unavoidable is that the species of Araucaria and Agathis that -survive, in some cases only in one or two small islands in the South -Pacific, have in the course of successive ages wandered from the other -end of the world. Their migrations can be partially traced by the -fragments embedded in Jurassic and later sediments, but we can only -speculate as to the causes which have contributed to the changes in the -fortunes of the family; how much influence may have been exerted by -changes in physical conditions in the environment, and to what extent -the production of more successful types may have been the dominant -cause of the decline, it is impossible to say. One thing at least is -certain, that few existing plants are better entitled to veneration as -survivals from the past than are the living species of Araucaria. - - - - -CHAPTER VIII - -THE MAIDEN HAIR TREE - - '...the trees - That whisper round a temple become soon - Dear as the temple's self.' - Keats. - -The Maiden Hair tree of China and Japan, which was introduced into -Europe early in the eighteenth century, has now become fairly well -known. Though hardy in England, it requires warmer summers for full -development and regular flowering. To botanists this Eastern tree is of -peculiar interest, partly because of the isolated position it occupies -in the plant-kingdom and partly by reason of its great antiquity. There -is probably no other existing tree which has so strong a claim to be -styled a 'living fossil,' to use a term applied by Darwin to survivals -from the past. In 1712 the traveller Kaempfer proposed for this plant -the generic name Ginkgo, and Linnaeus adopted this designation, adding -the specific name _biloba_ to denote the bisection of the wedge-shaped -lamina of the leaf into two divergent segments. In 1777 the English -botanist Sir J. E. Smith expressed his disapproval of what he called -the uncouth name Ginkgo by substituting for _Ginkgo biloba_ the title -Salisburia adiantifolia, but as it is customary to retain names adopted -or proposed by Linnaeus, the founder of the binominal system of -nomenclature, the correct botanical designation of the maiden hair tree -is _Ginkgo biloba_. Mere personal preference such as that of Sir J. E. -Smith for Salisburia is not an adequate reason for rejecting an older -name. - -[Illustration: Fig. 19. _Ginkgo biloba_ Linn. (Slightly reduced.)] - -In its pyramidal habit Ginkgo agrees generally with the larch and other -Conifers. Like the larch and cedar it possesses two kinds of foliage -shoots, the more rapidly growing long shoots with scattered leaves -and the much shorter dwarf-shoots which elongate slightly each year -and bear several leaves crowded round their apex. The leaves (Fig. -19), which are shed each year, are similar in the cuneate form of the -lamina and in the fan-like distribution of the forked veins, to the -large leaflets of some species of maiden hair ferns: the thin lamina -carried by a slender leaf-stalk is usually about 3 inches across, -though in exceptional cases it may reach a breadth of 8 inches. The -lamina is usually divided by a deep =V=-shaped sinus into two equal -halves; it may be entire with an irregularly crenulate margin, or, on -seedlings and vigorous long shoots, the lamina may be cut into several -wedge-shaped segments. - -The male and female flowers are borne on separate trees; the male -consists of a central axis giving off slender branches, each of which -ends in a small terminal knot and two elliptical capsules in which -the pollen is produced. The female flowers have a stouter axis which -normally produces two seeds at the apex. The seed is encased in a -green fleshy substance and, as in the fruit of a cherry or plum, the -kernel is protected by a hard woody shell. In the form of the leaves -and in the structure of the flowers Ginkgo presents features which -clearly distinguish it from the Conifers, the class in which, until -recently, it was included. In 1896 the Japanese botanist Hirase made -the important discovery that the male reproductive cells of Ginkgo are -large motile bodies provided with a spirally coiled band of minute -cilia--delicate hairs which by their rapid lashing-movement propel the -cell through water. In all Flowering Plants and in Conifers the male -reproductive cells have no independent means of locomotion; they are -carried to the female cell by the formation of a slender tube--the -pollen-tube--produced by the pollen-grain. In the Ferns, Lycopods and -Horsetails--in fact in all members of the Pteridophyta--as also in the -Mosses and Liverworts as well as in many of the still lower plants, -the male cells swim to the egg by the lashing of cilia like those on -the male cells of Ginkgo. This difference in regard to the nature of -the male cells was considered to be a fundamental distinction between -the higher seed-bearing plants and all other groups of the vegetable -kingdom. It was, therefore, with no ordinary interest that Hirase's -discovery was received, as it broke down a distinction between the two -great divisions of the plant-world which had been generally accepted -as fundamental; though it is only fair to say that the German botanist -Hofmeister, a man of exceptional originality and power of grasping the -essential, foresaw the possibility that this arbitrary barrier would -eventually be removed. The Ferns and other plants in which the male -cells are motile, represent earlier stages in the progress of plant -development, when the presence of water was essential for the act -of fertilisation, a relic of earlier days when the whole plant-body -was fitted for a life in water. As higher types were produced, the -plant-machinery became less dependent on an aqueous habitat, and the -loss of organs of locomotion in the male cells is an instance of the -kind of change accompanying the gradual adaptation to life on land. The -idea of the gradual emancipation of plants from a watery environment is -expressed in a somewhat extreme form by the author of a book entitled -_The Lessons of Evolution_(52), who states that the ocean is the mother -of plant-life and that plants formed the army which conquered the land. -In Ginkgo we have a type which, though similar in most respects to -the Conifers, possesses in its motile reproductive cells a persistent -inheritance from the past. The recognition of this special feature -afforded a sound reason, especially when other peculiarities are -considered, for removing Ginkgo from the Conifers and instituting a new -class-name, Ginkgoales. - -Ginkgo is a generalised type, linked by different characters both -with living members of the two classes of naked-seeded plants and -with certain existing Palaeozoic genera. It is a survivor of a race -which has narrowly escaped extinction; the last of a long line that -has outlived its family and offers by its persistence an impressive -instance of the past in the present. Though Mrs Bishop in her -_Untrodden Paths in Japan_ speaks of forests of Maiden Hair trees -apparently in a wild state, it is generally believed that they were -cultivated specimens. Mr Henry who has an exceptionally wide knowledge -of Chinese vegetation tells us that 'all scientific travellers in -Japan and the leading Japanese botanists and foresters deny its being -indigenous in any part of Japan; and botanical collectors have not -observed it truly wild in China.' Moreover, Mr E. H. Wilson, after -traversing the whole of the district where Ginkgo was supposed to occur -in a wild state, says that he found only cultivated trees. There is no -reason to doubt that China is the last stronghold of this ancient type -which in an earlier period of the earth's history overspread the world. - -A brief summary of the past history of Ginkgo and of the Ginkgoales -supplies overwhelming testimony to the tenacity of life with which the -Maiden Hair tree has persisted through the ages. - -It was pointed out in the account of the past history of Araucaria that -the records obtained from Palaeozoic rocks, while affording evidence of -the existence of Carboniferous and Permian genera undoubtedly allied -to the living species, do not enable us to speak with certainty as to -the precise degree of affinity. Similarly, Palaeozoic leaves have been -described as representatives of the class of which Ginkgo is the sole -survivor, but the evidence on which this relationship is assumed is by -no means conclusive. - -The generic name Psygmophyllum has been applied to some impressions -of Ginkgo-like leaves discovered in the Upper Devonian rocks of -Bear Island, a small remnant of land in the Arctic circle, which -has furnished valuable information as to the composition of one of -the oldest floras of which satisfactory remains have been found. -Other examples of these lobed, wedge-shaped leaves are recorded from -Carboniferous rocks in Germany, France, and elsewhere; from Permian -strata in the east of Russia and from Palaeozoic beds in Cape Colony -and Kashmir. A relationship between Psygmophyllum and Ginkgo is, -however, by no means established and rests solely on a resemblance in -the form of the leaves. The close correspondence in form and venation -between some leaves from Permian rocks in the Ural mountains and -from Lower Permian beds in France, and those of the recent species, -is considered by some authors sufficiently striking to justify the -reference of these fossils to the genus Ginkgo. Similar leaves of -Permian age, which may also be related to the existing species, have -been described under the name Ginkgophyllum. Other specimens of -Palaeozoic age from North America and elsewhere have been assigned to -the Ginkgoales; but in none of these cases, despite the resemblance -in leaf-form, is there sufficiently convincing evidence of close -relationship to warrant a definite assertion that the plants in -question were members of the group of which Ginkgo alone remains. - -It is, however, an undoubted fact that the Maiden Hair tree is -connected by a long line of ancestors with the earliest phase of the -Mesozoic era. From many parts of the world large collections of fossil -plants have been obtained from strata referred to the Rhaetic period, -or to the upper division of the Triassic system. A comparison of floras -from these geological horizons in different parts of the world points -to a vegetation extending from Australia, Cape Colony, and South -America, to Tonkin, the south of Sweden and North America, which was -characterised by a greater uniformity than is shown by widely separated -floras at the present day. One of the commonest genera in Rhaetic -floras is that known as Baiera; this name is applied to wedge-shaped -leaves with a slender stalk similar in shape and venation to those of -Ginkgo, but differing in the greater number and smaller breadth of -the segments. Between the deeply dissected leaf of a typical Baiera -with its narrow linear lobes and the entire or broadly lobed leaf of a -Ginkgo there are many connecting links, and to some specimens either -name might be applied with equal fitness. Examples of Baiera leaves, -in some cases associated with fragments of reproductive organs, are -recorded from Rhaetic rocks of France, the south of Sweden, Tonkin, -Chili, the Argentine, North America, South Africa, and from other -regions. There is abundant evidence pointing to the almost world-wide -distribution of the Ginkgoales, as represented more especially by -Baiera, in the older Mesozoic floras. In the later Jurassic rocks of -Yorkshire true Ginkgo leaves as well as those of the Baiera type are -fairly common; with the leaves have been found pieces of male and -female flowers. Ginkgo and Baiera have been described from Jurassic -rocks of Germany, France, Russia, Bornholm, and elsewhere in Europe; -they occur abundantly in Middle Jurassic rocks in northern Siberia, and -are represented in the Jurassic floras of Franz Josef Land, the East -Coast of Greenland, and Spitzbergen (Fig. 20). The abundance of Ginkgo -and Baiera leaves associated with male flowers and seeds discovered in -Jurassic rocks, approximately of the same geological age as those on -the Yorkshire coast, in East Siberia and in the Amur district, has led -to the suggestion that this region may have been a centre where the -Ginkgoales reached their maximum development in the Mesozoic period. - -[Illustration: Fig. 20. Fossil Ginkgo leaves. (1/2 nat. size.) - - A. Tertiary, Island of Mull. - B. Wealden, North Germany (after Schenk). - C. Jurassic, Japan (after Yokoyama). - D. Jurassic, Australia (after Stirling). - E. Jurassic, Siberia (after Heer). - F. Jurassic, Turkestan. - G. Lower Cretaceous, Greenland (after Heer). - H. Jurassic, California (after Fontaine). - I. Jurassic, Yorkshire. - J. Jurassic, N.E. Scotland (after Stopes). - K. Wealden, Franz Josef Land (after Nathorst). - L. Rhaetic, South Africa. - M. Jurassic, Spitzbergen (after Heer). - -] - -It should be added that other genera of Jurassic and Rhaetic fossils -in addition to Ginkgo and Baiera have been referred to the Ginkgoales, -though evidence of such affinity is not convincing. There is, however, -good reason to believe that this widespread group was represented by -several genera in the older Mesozoic floras. - -The occurrence of the Ginkgoales in Jurassic rocks in King Charles -Land and in the New Siberian Islands (lat. 78° and 75° N.), in Central -China, Japan, Turkestan, California, Oregon, South Africa, Australia, -and Graham's Land demonstrates the cosmopolitan nature of the group. -During the later part of the Jurassic period and in the Wealden floras -both Baiera and Ginkgo were abundant; leaves are recorded from Jurassic -strata in the north-east of Scotland, from Lower Cretaceous or Wealden -rocks in North Germany, Portugal, Vancouver Island, Wyoming, and -Greenland. - -During the Tertiary period, or probably in the earlier days of -that era. Ginkgo flourished in North America, in Alaska and in the -Mackenzie River district, Greenland, Saghalien Island, and in several -European regions. In Chapter III reference was made to the volcanic -activity which characterised the north-west European area in the -early Tertiary period and resulted in the formation of the thick -sheets of basalt on the north-east coast of Ireland and in the Inner -Hebrides. There were occasional pauses in the volcanic activity, -during which vegetation established itself on the weathered surface -of the lava, and left traces of its existence in the leaves and twigs -preserved in the sedimentary material enclosed between successive -lava-floras. At Ardtun Head in the Isle of Mull beautifully preserved -leaves of Ginkgo, 2-4 inches in breadth, with the median sinus and -the venation characteristic of the leaves of the existing plant, -have been discovered in a bed of clay which marks the site of a -lake in a depression on the lava-plateau. The resemblance of these -Tertiary leaves from Mull to those of the surviving Maiden Hair tree -is so close as to suggest specific identity. Mr Starkie Gardner and -Baron Ettingshausen have described some seeds from the London clay -(Lower Tertiary) in the Isle of Sheppey as those of Ginkgo, but this -identification rests on data too insufficient to be accepted without -hesitation. - -The recent cultivation of _Ginkgo biloba_ in Britain may therefore -be spoken of as the re-introduction of a plant which in the earlier -part or in the middle of the Tertiary period flourished in the west of -Scotland, and was abundant in England in the earlier Jurassic period. -It is impossible to say with any confidence where the Ginkgoales first -made their appearance, whether in the far north or in the south, nor -are we able to explain the gradual decline of so venerable and vigorous -a race. - -As we search among the fragmentary herbaria scattered through the -sedimentary rocks in that comparatively small portion of the earth's -crust which is accessible to investigation, we discover evidence of a -shifting of the balance of power among different classes of plants in -the course of our survey of successive floras. Plants now insignificant -and few in number are found to be descendants of a long line of -ancestors stretching back to a remote antiquity when they formed the -dominant class. Others which flourished in a former period no longer -survive, either themselves or in direct descendants. 'The extinction of -species has been involved in the most gratuitous mystery.' We can only -speculate vaguely as to the cause of success or failure. Certain types -were better armed for the struggle for life, and produced descendants -able to hold their own and to perpetuate the race through the ages in -an unbroken line. Others had a shorter life and fell out of the ranks -of the advancing and ever changing army. To quote Darwin's words:'We -need not marvel at extinction; if we must marvel, let it be at our -own presumption in imagining for a moment that we understand the many -complex contingencies on which the existence of each species depends.' - - - - -BIBLIOGRAPHY - - -Many of the books and papers dealing with subjects touched upon in -this volume are not included in the following list. For reference to -a more complete bibliography the reader should consult more technical -treatises. - - 1. Holmes, T. Rice. Ancient Britain and the invasions of Julius - Caesar. Oxford, 1907. - - 2. Mitchell, A. The Past in the Present; what is Civilisation? - Edinburgh, 1880. - - 3. Weismann, A. Essays upon Heredity and Kindred Biological - Problems, (I. The Duration of Life.) Vol. I. Edited by E. B. - Poulton, S. Schönland, and A. E. Shipley. (Second Edition.) - Oxford, 1891. - - 4. The Historie of the World, commonly called the Naturall - Historic of the C. Plinius Secundus. Translated into English by - Philemon Holland. London, 1634. - - 5. Hooker, J. D. On Three Oaks of Palestine. _Trans. Linnean - Society_, Vol. XXIII. p. 381. 1862. - - 6. Holtermann, Carl. Der Einfluss des Klimas auf den Bau der - Pflanzengewebe. Leipzig, 1907. - - 7. Atkinson, A. Notes on an Ancient Boat found at Brigg. - _Archaeologia_, Vol. I. p. 361. 1887. - - 8. Huxley, T. H. Man's Place in Nature and other Anthropological - Essays. _Collected Essays_, Vol. VII. (On the methods and - results of Ethnology.) London, 1901. - - 9. Lewis, F. J. The sequence of Plant Remains in the British Peat - Mosses. _Science Progress_, No. 6. October, 1907. - - 10. Strahan, A. On submerged Land-surfaces at Barry, Glamorganshire. - With notes on the Fauna and Flora by Clement Reid; etc. _Quart. - Journ. Geological Society_, Vol. LII. p. 474. 1896. - - 11. The Life and Letters of Charles Darwin. Edited by Francis - Darwin. 3 Vols. London, 1887. - - 12. More Letters of Charles Darwin. Edited by Francis Darwin and A. - C. Seward. 2 Vols. London, 1903. - - 13. Ward, Lester F. The Course of Biologic Evolution. Anniversary - Address of the President of the Biological Society. Washington, - 1890. - - 14. Marshall, W. _Anacharis alsinastrum_, a new water weed. - (Reprinted from the Cambridge _Independent Press_.) London, 1852. - - { Bailey, C. Notes on the structure, the occurrence in - { Lancashire, and the source of origin, of _Naias gramineus_ - { Delile, var. _Delilei magnus_. _Journal of Botany_, - { Vol. XXII. p. 305. 1884. - 15. { - { Weiss, F. H. and H. Murray. On the occurrence and - { distribution of some alien aquatic plants in the Reddish - { Canal. _Mem. Proc. Manchester Lit. and Phil. Society_, - { Vol. LIII. Pt. II. 1909. - - 16. Bennett, A. The Halifax Potamogeton. _Naturalist_, No. 621. - October, 1908. - - 17. Hooker, J. D. Outlines of the Distribution of Arctic Plants. - _Trans. Linn. Soc._ Vol. XXIII. p. 251. 1862. - - 18. Engler, A. Plants of the Northern Temperate Zone in their - transition to the High Mountains of Tropical Africa. _Annals of - Botany_, Vol. XVIII. p. 523. 1904. - - 19. Darwin, C. The Origin of Species. London, 1900. - - 20. Ridley, H. N. On the dispersal of seeds by wind. _Annals of - Botany_, Vol. XIX. p. 351. 1905. - - 21. Hooker, J. D. On the Cedars of Lebanon, Taunus, Algeria, and - India. _The Natural History Review_, 1862, p. 11. - - 22. Forbes, E. On the connection between the distribution of - the existing Fauna and Flora of the British Isles, and the - geological changes which have affected their area.... _Memoirs, - Geological Survey_, Vol. I. p. 336. 1846. - - 23. Praeger, R. L. The Wild Flowers of the West of Ireland and their - history. _Journ. R. Hort. Soc._ Vol. XXXVI. p. 299. 1910. - - 24. Ernst, A. The New Flora of the Volcanic Island of Krakatau. - Translated by A. C. Seward. Cambridge, 1908. - - 25. Praeger, R. L. A Tourist's Flora of the West of Ireland. Dublin, - 1909. - - { Rendle, A. B. _Sisyrinchium californicum_ Dryand. - 26. { _Journal of Botany_, Vol XXXIV. p. 494. 1896. - { Marshall, E. S. _Sisyrinchium californicum_ in Ireland. - { _Ibid._ p. 366. - - { Reid, Clement. The Origin of the British Flora. London, 1899. - 27. { Reid, Clement and Eleanor M. On the Pre-glacial - { Flora of Britain _Journ. Linn. Soc._ Vol. XXVIII. p. 206. - { 1908. - - 28. Lankester, Sir Edwin Ray. Mature and Man. The Romanes Lecture. - Oxford, 1905. - - 29. Huxley, T. H. On a Piece of Chalk. _Collected Essays_, Vol. - VIII. London, 1896. - - 30. Jukes-Browne, A. J. The Building of the British Isles. London, - 1911. - - 31. Ray, J. Three Physico-Theological Discourses, etc. (2nd - Edition.) London, 1693. - - 32. Woodward, J. An Essay toward a Natural History of the Earth. - London, 1695. - - 33. Sollas, W. J. The Age of the Earth, and other geological - studies. London, 1905. - - 34. Ward, L. F. Status of the Mesozoic Floras of the United States. - _Monograph 48, U. S. Geol. Surv._ 1905. - - 35. Arber, E. A. Newell. _Cupressinoxylon Hookeri_ sp. nov., a large - silicified tree from Tasmania. _Geological Magazine_, Vol. I. - [V.], p. 7. 1904. - - { 1. Holmes, W. H. Fossil Forests of the Volcanic Tertiary - { Formations of the Yellowstone National Park. Ann. - { Rep. Geol. and Geogr. Surv. (U.S.A.), 1878, Pt. II. p. 47. - 36. { 2. Knowlton, F. H. Fossil Flora of the Yellowstone - { National Park. _Monograph 32, U. S. Geol. Survey_, - { Pt. II. 1899. - - 37. Darwin, C. Journal of Researches into the Natural History and - Geology of the countries visited during the voyage round the - world of H.M.S. 'Beagle.' London, 1902. - - 38. Dufferin, Lord. Letters from High Latitudes. London. N.D. - - 39. Amundsen, R. The North-West Passage. 2 Vols. London,. 1908. - - 40. MacDougal, D. T. Botanical Explorations in the South-west. - _Journ. New York Botanical Garden_, Vol. V. p. 89. 1904. - - { Goeppert, H. R. and A. Menge. Die Flora des Bernsteins. - 41. { Danzig, 1883. - { Conwentz, H. Monographie der baltischen Bernsteinbäume. - { Danzig, 1890. - - 42. Hovelacque, M. Sur la Nature végétale de l'_Aachenosaurus - multidens._ _Bull. Soc. Belge de Géol._ etc. Tome IV. p. 59. - 1890. - - 43. Oliver, F. W. and D. H. Scott. On the structure of the - Palaeozoic seed _Lagenostoma Lomaxi_. _Phil. Trans. R. Soc._ - Vol. CXCVII. p. 193. 1904. - - 44. Kidston, R. On the fructification of _Neuropteris heterophylla_. - _Phil. Trans. Royal Soc. London_, Vol. CXCVII. p. 1. - - 45. Smith, Geoffrey. A Naturalist in Tasmania. Oxford, 1909. - - 46. Campbell, D. H. On the Distribution of the Hepaticae, and its - significance. _New Phytologist_, Vol. VI. p. 203. 1907. - - 47. Kidston, R. and D. T. Gwynne-Vaughan. On the Fossil Osmundaceae. - Phil. Trans. R. Soc. Edinburgh, Vols. XLV., XLVI. 1907-09. - - 48. Seward, A. C. Fossil Plants. 2 Vols. Cambridge, 1898-1910. - - 49. Wallace, A. R. The Malay Archipelago. London, 1886. - - 50. Reid, C. and Eleanor M. The Lignite of Bovey Tracey. _Phil. - Trans. Royal Soc. London_, Vol. 201, p. 161. 1910. - - 51. Hollick, A. and E. C. Jeffrey. Studies of Cretaceous Coniferous - remains from Kreischerville, New York. _Mem. New York Bot. - Garden_, Vol. III. 1909. - - 52. Hutton, F. W. The Lessons of Evolution. London, 1902. - - - - -INDEX - - - _Aachenosaurus multidens_, 68 - _Agathis australis_, 107 - _A. Moorei_, 108 - _A. robusta_, 108, 109 - Amber, 65, 66 - Amethyst Mountain, 59, 60, 104 - Amundsen, E., 62 - _Anacharis alsinastrum_, 20 - Angiosperms, history of, 16, 53, 69, 70 - Annual rings, 5-9 - Antarctic fossil plants, 70, 117 - _Araucaria Bidwillii_, 115 - _A. brasiliana_, 109 - _A. Cookii_, 111, 118 - _A. excelsa_, 110, 111, 114, 115, 118 - _A. imbricata_, 109, 111, 113, 118 - Araucarieae, 106-120 - Araucarioxylon, 112 - _Araucarites Oldhami_, 113 - _A. sphaerocarpus_, 116 - Arbutus Unedo, 31-33, 36 - Archaean rocks, 43 - Arctic plants, 22, 23, 30, 69, 127 - Arctic-Alpine plants, 22, 23 - Arizona, fossil forests of, 59 - Artocarpus, 28, 29 - - Baiera, 129, 131 - Banks, Sir Joseph, 110 - Barry, forest beds at, 13 - Bennett, A., 21 - _Bidens tripartita_, 46, 47 - Bishop, Mrs, 126 - Bommer, C, 73, 82, 89 - Bovey Tracey, fossil plants from, 101-103 - Bower, Prof., 73 - Bracken Fern, 75, 77, 83, 87 - Brandon, flint-knappers of, 3 - Brigg, dug-out boat from, 10, 11 - British flora, 19-38 - - _Caltha palustris_, 47 - Campbell, Prof. D. H., 79 - Candolle, A. P. de, 7, 33 - Canton, W., 34 - Carboniferous plants, 66-68, 72-75, 127 - Carruthers, Dr W., 115 - Cedars, 27 - Cheddar Pink, 24 - _Cinnamomum prototypum_, 65, 66 - Climate, fossil plants and, 68, 69 - Coal age, plants of the, 19, 66, 67 - Connemara, 30, 31 - Cook, Capt., 111 - Coral polyps compared with plants, 8 - Cordaites, 112 - Cornwall, Pyrenean Heaths in, 31 - Cretaceous plants, 16, 17, 53, 82, 117 - Cromer Forest bed, 48 - _Cryptomeria japonica_, 111 - Cycads, 11, 72-74 - - _Daboecia polifolia_, 30 - Dacrydium, 85 - Dakota group, flora of, 17 - _Dammara alba_, 107 - Darwin, C, 16, 24, 25, 33, 39, 40, 61, 133 - Devonshire, Pyrenean Heaths in, 31 - _Dianthus caesius_, 24 - Dipteris, 77, 92-94 - _D. conjugata_, 92, 93 - _D. Horsfieldii_, 86, 93 - Disco Island, Fossil plants from, 28, 69, 82, 103 - Discontinuous distribution, 26 - Dispersal of plants, rate of, 25, 26 - Distribution of plants, 15-38 - Drift-wood, 61-63 - _Dryas octopetala_, 22 - Dufferin, Lord, 61 - - _Elodea canadensis_, 20, 21 - Engler, Prof., 23 - _Erica ciliaris_, 31 - _E. Mackaii_, 31 - _E. mediterranea_, 30, 31 - _E. vagans_, 31 - _Eriocaulon septangulare_, 35-38 - Ettingshausen, Baron, 105, 132 - - Ferns, 71-94 - Flowering plants, see Angiosperms - Forbes, E., 31-34, 37 - Fossil plants, as thermometers, 68; - preservation of, 56-70 - - Gardner, J. S., 132 - Geographical distribution of plants, 15-38 - Geological evolution of Britain, 29 - Geological record, 39-55 - Geological table, 42, 43 - Geological time, 2, 3, 49 - _Ginkgo biloba_, 113, 120-133 - Ginkgoales, 18, 120-133 - Ginkgophyllum, 128 - Glacial period, effect on vegetation of, 29-32, 45, 47 - _Gladiolus illyricus_, 31 - Gleichenia, 81-83 - Graham's Land, 70, 117 - Gunn, Dr Marcus, 117 - Gwynne-Vaughan, Prof., 80 - Gymnosperms, 17, 18 - - _Habenaria intacta_, 37 - Halifax, plants from canal near, 21 - Heer, O.,33, 82, 101 - Henry, A., 126 - Hirase, Prof., 124, 125 - Hofmeister, W. F. B., 125 - Hollick, A., 119 - Holmes, T. Rice, 2 - Hooker, Sir J. D., 4, 15, 16, 22, 23, 27, 40 - Hose, C, 87 - Huxley, T. H., 11, 52 - - Ireland, Mediterranean plants in, 30-38 - - Jeffrey, Prof. E. C, 114, 119 - Jet, 114 - Juan Fernandez, 84 - Jurassic flora, 53, 54, 70, 117 - Jussieu, A. de, 109 - - Kaempfer, E., 121 - Kauri Pine, 107 - Kidston, Dr E., 74, 80 - Knaresborough, petrifying spring at, 64 - Krakatau, new flora of, 33, 31 - - Laccopteris, 90, 91 - Lang, Dr A. , 27 - Lankester, Sir Edwin Ray, 49 - Lhwyd, E., 57 - Linnaeus, C, 121, 123 - Liriodendron, 28, 29 - Liverworts, antiquity of, 79 - London Pride, 31 - Longevity of trees, 1-10 - _Luzula racemosa_, 23 - _L. spicata_, 23, 24 - - MacDougal, Prof., 62 - Maiden Hair Tree, 120-133 - Mammoth trees of California, 95-105 - Man, first appearance of, 49 - Marchantia, 79 - Market Harborough, Elodea discovered near, 20 - Marshall, E. S., 38 - Matonia, 77, 86-94 - _M. pectinata_, 86-88, 92, 93 - _M. sarmentosa_, 87 - Matonidium, 89 - Mediterranean plants in Ireland, 30-38 - Miller, Hugh, 59, 115, 117 - Milligan, Dr, 2 - Moss, Dr C. E., 23 - Mull, Fossil plants in Isle of, 132 - - _Naias graminea_, 21 - Nathorst, A. G., 64, 103, 117 - Native plants, 20 - New forest, 31 - _Nipa fruticans_, 50-52 - Nipadites, 50, 52 - Norfolk Island Pine, see _Araucaria excelsa_ - - Oaks, longevity of, 4 - Oliver, Prof. F. W., 74 - _Osmunda regalis_, 76-79, 83 - _Osmundites Dunlopi_, 80 - - Palaeozoic plants, 55, 66-68, 71, 127, 128 - Peat, trees in, 12, 13 - Permian floras, 55 - Petrifaction, 64-67 - _Picea excelsa_, 46, 48 - Pines, Tertiary, 65, 66 - _Pinus sylvestris_, 11-13, 47 - Pipewort, 36-38 - Pliny's Natural History, 4 - Podocarpus, 109 - _Potamogeton pennsylvanicus_, 21 - Praeger, E. L., 32, 36, 37 - Pre-Glacial plants, 22, 45-48 - _Primula elatior_, 24 - Protodammara, 119 - Psygmophyllum, 127 - _Pteridium aquilinum_, 75, 77, 83, 87 - Pteridophyta, 18, 124 - Pteridosperms, 74, 75 - Pyrenean plants in Ireland, 31-38 - - Ray, John, 56 - Reddish Canal, plants from the, 21 - Redwoods of California, 95-105 - Reid, Clement, 13, 22, 45, 102 - Reid, Mrs, 22, 102 - Rhaetic plants, 54, 94 - Riccia, 79 - Ridley, H. N., 25 - Royal Fern, 76-79, 83 - _Rubus chamaemorus_, 22 - - St Dabeoc's Heath, 30, 32, 37 - _Salisburia adiantifolia_, 122 - Saporta, the Marquis of, 70 - _Saxifraga oppositifolia_, 22 - _S. umbrosa_, 31 - Scandinavian plants in Britain, 21-23, 30 - Scots Pine, see _Pinus sylvestris_ - Scott, Dr D. H., 74 - Sequoia, 5, 95-105 - _Sequoia Couttsiae_, 101 - _S. gigantea_, 5, 95, 96, 98-104 - _S. magnifica_, 104 - _S. novae zeelandicae_, 105 - _S. sempervirens_, 45, 96, 98, 104 - Sheppey, fossil plants from, 50, 132 - _Shorea leprosula_, 25 - _Silene acaulis_, 22 - _Sisyrinchium angustifolium_, 38 - _S. californicum_, 38 - Smith, G., 75 - Smith, Sir J. E., 122, 123 - Smith, W., 41 - Sollas, Prof., 58 - _Spiranthes romanzoffiana_, 38 - _Stellaria holostea_, 46, 47 - Steno, 57 - Strahan, A., 13 - Strawberry tree, 31, 32 - - Tansley, A. G., 12, 13, 87 - _Taxodium distichum_, 103 - Tertiary plants, 31-33, 37, 49, 50, 103 - _Theobroma cacao_, 7 - _Thyrsopteris elegans_, 84 - _Todea barbara_, 11, 78 - _T. radicans_, 78 - _Trapa natans_, 47, 48 - Triassic period, 54, 55 - Tulip tree, 28 - - Walchia, 113 - Wallace, Dr A. R., 85 - Wealden flora, 17, 53 - Weismann, A., 3 - Wexford, American plant from, 38 - Williamson, Prof. W. C, 72 - Wilson, E. H., 120 - Winchester Cathedral, wood from foundations of, 10 - Woodward, Dr J., 57 - Woodworthia, 114 - - Yellowstone Park, fossil trees in the, 59-61, 104 - - Zeiller, R., 113 - -CAMBRIDGE: PRINTED BY JOHN CLAY, M.A. AT THE UNIVERSITY PRESS - - - THE CAMBRIDGE MANUALS OF SCIENCE AND LITERATURE - Published by the Cambridge University Press - - Price 1s net each in cloth - 2s 6d net in lambskin - - GENERAL EDITORS - P. GILES, Litt.D. Master of Emmanuel College - and - A. C. 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You may copy it, give it away or re-use it under the terms of -the Project Gutenberg License included with this eBook or online at -www.gutenberg.org. If you are not located in the United States, you'll have -to check the laws of the country where you are located before using this ebook. - -Title: Links With the Past in the Plant World - -Author: Albert Charles Seward - -Release Date: June 29, 2020 [EBook #62521] - -Language: English - -Character set encoding: ISO-8859-1 - -*** START OF THIS PROJECT GUTENBERG EBOOK LINKS WITH PAST IN PLANT WORLD *** - - - - -Produced by Tom Cosmas - - - - - -</pre> - - - - - - -<div class="fig_center" style="width: 263px;"> -<img src="images/cover.jpg" width="263" height="393" alt="Links With the Past in the Plant World by A. C. Seward" /> -</div> - - -<hr class="chap" /> - - - -<p><span class="pagenum"><a name="Page_i" id="Page_i"> i </a></span></p> - -<p class="caption3nb">The Cambridge Manuals of Science and -Literature</p> - -<h1 class="pmt4 pmb4">LINKS WITH THE PAST IN<br /> -THE PLANT WORLD</h1> - - -<p class="center"><span class="pagenum"><a name="Page_ii" id="Page_ii"> ii </a></span></p> - -<p class="center">CAMBRIDGE UNIVERSITY PRESS</p> - -<p class="center"><span class="antiqua">London</span>: FETTER LANE, E.C.</p> - -<p class="center">C. F. CLAY, <span class="smcap">Manager</span></p> - -<div class="fig_center" style="width: 73px;"> -<img src="images/page_ii.png" width="73" height="78" alt="" /> -</div> - -<hr class="chap" /> - -<div style="width: 30em; margin:auto;"> - -<p><span class="antiqua">Edinburgh</span>: 100, PRINCES STREET</p> - -<p><span class="antiqua">London</span>: H. K. LEWIS, 136, GOWER STREET, W.C.</p> - -<p><span class="antiqua">Berlin</span>: A. ASHER AND CO.</p> - -<p><span class="antiqua">Leipzig</span>: F. A. BROCKHAUS</p> - -<p><span class="antiqua">New York</span>: G. P. PUTNAM'S SONS</p> - -<p><span class="antiqua">Bombay and Calcutta</span>: MACMILLAN AND CO., <span class="smcap">Ltd</span>.</p> -</div> - - -<p class="center pmb2"><i>All rights reserved</i></p> - -<hr class="chap" /> - -<p><span class="pagenum"> <a name="Page_iii" id="Page_iii"> iii </a></span></p> - -<p><span class="pagenum"> <a name="Page_iv" id="Page_iv"> iv </a></span></p> - -<div class="fig_center" style="width: 364px;"> -<img src="images/page_iv.png" width="364" height="469" alt="" /> -<div class="fig_caption"><i>Sequoia magnifica</i> Knowlton, in the Yellowstone National Park. -(From a photograph kindly supplied by Prof. Knowlton.) See <a href="#Page_104">p. 104</a>.</div> -</div> - -<hr class="chap" /> - -<p><span class="pagenum"><a name="Page_v" id="Page_v"> v </a></span></p> - - - -<div class="fig_center" style="width: 415px;"> -<img src="images/page_v.png" width="415" height="636" alt="" /> -</div> - -<div style="width: 20em; margin:auto;"> -<p class="pmt2 bbox center smaller"> -LINKS WITH THE<br /> -PAST IN THE<br /> -PLANT WORLD<br /> -<br /> -BY<br /> -<br /> -A. C. SEWARD,<br /> -M.A., F.R.S.<br /> -<br /> -Professor of Botany in the<br /> -University of Cambridge<br /> -<br /> -Cambridge:<br /> -at the University Press<br /> -<br /> -1911 -</p> -</div> - -<p><span class="pagenum"><a name="Page_vi" id="Page_vi"> vi </a></span></p> - -<p class="pmt4 center"><span class="antiqua">Cambridge</span>:</p> - -<p class="pmb4 center">PRINTED BY JOHN CLAY, M.A.<br /> -AT THE UNIVERSITY PRESS</p> - - -<p class="pmt4"><i>With the exception of the coat of arms at -the foot, the design on the title page is a -reproduction of one used by the earliest known -Cambridge printer, John Siberch, 1521</i></p> -<hr class="chap" /> - -<p><span class="pagenum"><a name="Page_vii" id="Page_vii"> vii </a></span></p> - - - -<h2><a name="PREFACE" id="PREFACE">PREFACE</a></h2> - - -<div class="dropcap">M</div> - -<p class="p0"><span class="hidden">M</span>Y object in writing this book is primarily to -call attention to some of the many questions -which are raised by an enquiry into the relative -antiquity of existing plants, and to illustrate the -nature of the evidence afforded by the records of -the rocks. One may agree with the dictum, 'There -is but one art—to omit,' but to practise this art is -often a difficult task. While fully conscious of the -incompleteness of the treatment of the subjects dealt -with in these pages, and of defects in the method of -presentation, I hope that I may succeed in attracting -some of my readers who are already interested in -living plants to the study of plants of former ages.</p> - -<p>I am greatly indebted to my colleague Dr C. E. -Moss for reading the proofs and for many valuable -<span class="pagenum"><a name="Page_viii" id="Page_viii"> viii </a></span> -suggestions. I wish to thank Mr and Mrs Clement -Reid, Prof. MacDougal of the Arizona Desert Laboratory, -Prof Campbell of Stanford University, Prof -F. H. Knowlton of the United States National -Museum, Washington, Mr A. G. Tansley, Prof Yapp, -and Mr W. R. Welch for photographs which they -have allowed me to reproduce. As on many previous -occasions, I am indebted to my wife for contributing -drawings.</p> - -<p class="tdr">A. C. SEWARD.</p> - -<p class="p0 tdl"><span class="smcap">Botany School, Cambridge.</span><br /> - <i>July 1911.</i></p> - - -<p>The numbers in brackets interspersed in the text refer to the -Bibliography at the end of the volume.</p> - -<hr class="chap" /> - -<p><span class="pagenum"><a name="Page_ix" id="Page_ix"> ix </a></span></p> - - - -<h2><a name="CONTENTS" id="CONTENTS">CONTENTS</a></h2> - - -<table summary="TOC"> -<tr> - <td></td> - <td></td> - <td class="smaller tdr">PAGE</td> -</tr> -<tr> - <td></td> - <td class="tdl"><span class="smcap">Preface</span></td> - <td class="smaller tdr">vii</td> -</tr> -<tr> - <td class="smaller">CHAP.</td> - <td></td> - <td></td> -</tr> -<tr> - <td class="tdr">I.</td> - <td class="tdl">Introductory: the Longevity of Trees, etc.</td> - <td class="tdr"><a href="#CHAPTER_I">1</a></td> -</tr> -<tr> - <td class="tdr">II.</td> - <td class="tdl">The Geographical Distribution of Plants</td> - <td class="smaller tdr"><a href="#CHAPTER_II">15</a></td> -</tr> -<tr> - <td class="tdr">III.</td> - <td class="tdl">The Geological Record</td> - <td class="tdr"><a href="#CHAPTER_III">39</a></td> -</tr> -<tr> - <td class="tdr">IV.</td> - <td class="tdl">Preservation of Plants as Fossils</td> - <td class="tdr"><a href="#CHAPTER_IV">56</a></td> -</tr> -<tr> - <td class="tdr">V.</td> - <td class="tdl">Ferns; their Distribution and Antiquity</td> - <td class="tdr"><a href="#CHAPTER_V">71</a></td> -</tr> -<tr> - <td class="tdr">VI.</td> - <td class="tdl">The Redwood and Mammoth Trees of California</td> - <td class="tdr"><a href="#CHAPTER_VI">95</a></td> -</tr> -<tr> - <td class="tdr">VII.</td> - <td class="tdl">The Araucaria family</td> - <td class="tdr"><a href="#CHAPTER_VII">106</a></td> -</tr> -<tr> - <td class="tdr">VIII.</td> - <td class="tdl">The Maiden Hair Tree</td> - <td class="tdr"><a href="#CHAPTER_VIII">121</a></td> -</tr> -<tr> - <td></td> - <td class="tdl">Bibliography</td> - <td class="tdr"><a href="#BIBLIOGRAPHY">134</a></td> -</tr> -<tr> - <td></td> - <td class="tdl">Index</td> - <td class="tdr"><a href="#INDEX">139</a></td> -</tr> -</table> - - -<p> <span class="pagenum"><a name="Page_x" id="Page_x"> x </a></span></p> - -<p> <span class="pagenum"><a name="Page_xi" id="Page_xi"> xi </a></span></p> - -<p> <span class="pagenum"><a name="Page_xii" id="Page_xii"> xii </a></span></p> - -<hr class="chap" /> - -<p class="caption3nb"><i>Links with the Past</i></p> - -<p class="caption3"><a id="ERRATUM"></a>ERRATUM</p> - -<p><a href="#Page_78">Page 78.</a> Omit lines 5, 6, and 7, from "One" to "but" inclusive.</p> - -<div style="margin: 0 3em;"> - -<p class="hanging">Transcriber Note: This correction has been applied. Here is the -original text with the changes indicated:—</p> - -<p><span style="text-decoration: line-through;">One filmy species of Todea is represented in the British flora by -<i>Todea radicans</i> in the Killarney district of Ireland; but t</span><span style="color: red;">T</span>he maximum -development of the genus is in New Zealand.</p> -</div> - - -<hr class="chap" /> - -<p><span class="pagenum"><a name="Page_1" id="Page_1"> 1 </a></span></p> - - - -<h2><a name="CHAPTER_I" id="CHAPTER_I">CHAPTER I</a></h2> - -<p class="caption3">INTRODUCTORY: THE LONGEVITY OF TREES, ETC.</p> - - - -<p class="smaller">'Believe me who have tried. Thou wilt find something more in -woods than in books. Trees and rocks will teach what thou canst -not hear from a master.' <span class="smcap">St Bernard.</span></p> - - -<p>The recent publication in the daily press of -instances of human longevity under the heading -'Links with the Past' prompted a comparison between -the length of time represented by the duration of a -tree and the lifetime of a human being. The comparison -of single lives suggested the further step of -contrasting the antiquity of the oldest family-histories -with the remoteness of the period to which it is -possible to trace the ancestry of existing members of -the plant kingdom.</p> - -<p>My primary object in these pages is not to deal with -familiar cases of longevity in trees, but to consider -in the first place some of the problems connected with -the origin of the present British flora, and then to -describe a few examples of different types of plants -<span class="pagenum"><a name="Page_2" id="Page_2"> 2 </a></span> -whose ancestors flourished during periods of the -earth's history long ages before the advent of the -human race.</p> - -<p>In dealing with plants of former ages we are -confronted with the difficulty of forming an adequate -conception of the length of time embraced by geological -periods in comparison with the duration of -the historic era. Some of the 'Selections from the -Greek Papyri' recently edited by Dr Milligan -(Cambridge 1910) refer to common-place events in -terms familiar to us in modern letters: we forget -the interval of 2000 years which has elapsed since -they were written. Similarly, the close agreement -between existing plants and species which lived in -remote epochs speaks of continuity through the ages, -and bridges across an extent of time too great to -be expressed by ordinary standards of measurement. -Terms of years when extended beyond the limits -to which our minds are accustomed cease to have -any definite meaning. While there is a certain -academic interest in discussions as to the age -of the earth as expressed in years, we are utterly -unable to realise the significance of the chronology -employed. After speaking of the futility of attempting -to introduce chronological precision into periods so -recent as those which come into the purview of -archaeologists, Mr Rice Holmes suggests a method -better adapted to our powers. He says—'Ascend -<span class="pagenum"><a name="Page_3" id="Page_3"> 3 </a></span> -the hill on which stands Dover Castle, and gaze -upon Cape Grisnez, let the waters beneath you -disappear; across the chalk that once spanned the -channel like a bridge men walked from the white -cliff that marks the horizon to where you stand. -No arithmetical chronology can spur the imagination -to flights like these(<a href="#Note_1">1</a>).' On the other hand, the -use in some country districts in Britain of spindles -almost identical with instruments used in spinning -by the ancient Egyptians, and similar survivals -described by the author of a book entitled <i>The -Past in the Present</i>(<a href="#Note_2">2</a>), bring within the range -of our vision an early phase of the historic era. -The rude implements still fashioned by the flint-knappers -of Brandon in Suffolk connect the present -with the Palaeolithic age. Measured from the -standpoint of historic reckoning, survivals from -prehistoric days appeal to us as persistent types -which have remained unchanged in a constantly -changing world.</p> - -<p>In one of his essays Weismann quotes an old -German saying with regard to comparative longevity, -which asserts that 'a wren lives three years, a dog -three times as long as a wren' and so on in a regularly -ascending series: the life of a deer is estimated -at three times that of a crow and an oak three times -that of a deer, which means that, computed on this -basis, an oak lives nearly 20,000 years(<a href="#Note_3">3</a>)! This -<span class="pagenum"><a name="Page_4" id="Page_4">[Pg 4]</a></span> -fanciful illustration of the relative longevity of an -oak is the expression of a truth, namely the superiority -of trees over animals in regard to the duration of -life. As a seventeenth-century translator of Pliny's -<i>Natural History</i> writes, 'In old times trees were the -very temples of the gods: and according to that -antient manner, the plaine and simple peasants of -the country, savouring still of antiquity, do at this -day consecrate to one God or other, the goodliest -and fairest trees that they can meet withal.' Oaks -growing in Pliny's day in the Hercynian forest are -said to have been there 'ever since the creation of -the world(<a href="#Note_4">4</a>).' Sir Joseph Hooker, in an account -of some Palestine oaks, gives a drawing of a famous -tree at Mamre, known as Abraham's Oak, which is -supposed to mark the spot where the Patriarch -pitched his tent(<a href="#Note_5">5</a>). Examples such as these, -though of no scientific value, serve to illustrate the -well-founded belief in the extraordinary longevity of -trees. In the absence of evidence to the contrary, it -would be rash to deny the possibility that William -the Conqueror's Oak in Windsor Forest, described -by Loudon in his <i>Arboretum Britannicum</i> and -mentioned by later writers, may be a survival from -the reign of the king whose name it bears. Although -it is seldom possible to state with confidence the -exact age of old oaks and yews famed for length of -days, there can be no doubt as to the enormous -<span class="pagenum"><a name="Page_5" id="Page_5"> 5 </a></span> -antiquity of many of our trees whose years are -'sacred with many a mystery.' The section of a -trunk of one of the mammoth trees of California -(<i>Sequoia gigantea</i>) exhibited in the Natural History -department of the British Museum, shows on its -polished surface 1335 concentric rings denoting -successive increments of wood produced by the -activity of a cylinder of cells situated between the -hard woody tissue and the bark. It is generally -assumed that each year a tree produces a single -ring, though, as is well known, an estimate of age -calculated on this assumption cannot be regarded as -more than an approximation to the truth. If this -giant tree, which was felled in 1890, was then 1335 -years old, it had already reached an age of over two -centuries when Charlemagne was crowned Emperor -at Rome. The concentric rings on a tree trunk owe -their existence to certain structural differences between -the wood formed in the spring and in the late -summer. In Sequoia, as in other members of the -great class of cone-bearing trees, the wood is composed -of comparatively narrow elements which serve -to carry water from the roots to the branches and -leaves. As spring succeeds winter the inactivity -of the plant-machine is followed by a period of -energetic life; opening buds and elongating shoots -create a demand for a plentiful supply of ascending -sap, and in response to this the tree produces a fresh -<span class="pagenum"><a name="Page_6" id="Page_6"> 6 </a></span> -cylinder of wood composed of relatively wide conducting -tubes. After the first rush of life is succeeded -by a phase of more uniform and gentler activity, the -demand for water becomes less exacting and the -wood which is formed during the rest of the growing -season consists of narrower water-pipes. A period of -rest ensues, until in the following spring new layers -of larger tubes are laid down in juxtaposition to the -narrower elements of the latest phase of the preceding -summer. This alternation of larger and smaller -tubes produces the appearance of concentric rings on -a cross-section of a tree. It is not the pause in the -active life of the plant which is responsible for the -effect of rings, but the fact that the wood produced -immediately before and immediately after the pause -is not structurally identical. In trees grown under -the more uniform conditions of certain tropical -regions, the annual rings are either feebly developed or -absent; for example, in some Indian oaks the wood -shows no concentric rings of growth.</p> - -<p>Stated in general terms, rings of growth in the -wood of a tree are the expression of a power possessed -by the plant of regulating the structure of its component -elements in response to the varying nature of -the external stimuli. In certain circumstances, for -example after the destruction of the young buds by -caterpillars, the tree makes a special effort to repair -the loss by producing a new set of shoots. This may -<span class="pagenum"><a name="Page_7" id="Page_7"> 7 </a></span> -be recorded by the occurrence of two concentric rings -in one season. An extreme instance of departure -from the normal has recently been described(<a href="#Note_6">6</a>) in -which a tree of <i>Theobroma cacao</i> (the cocoa tree), -planted in Ceylon in the summer of 1893 and felled -in January 1901, after a life of just over 7 years, was -found to have 22 rings in its stem. In this case the -tree shed its leaves three times a year, and each break -in the uniformity of its vital activities was registered -by the apposition of what under ordinary conditions -are spoken of as spring and late-summer wood. -At Aden trees stated by natives to be very old -showed only five or six rings of wood, a fact connected -with the almost complete lack of rain and with the -uniform conditions of existence.</p> - -<p>The degree of accuracy to be allowed to estimates -of age founded on the number of 'annual' rings is, -however, of secondary importance in comparison -with the enormously greater hold on life possessed -by trees as contrasted with the higher animals. Early -in the nineteenth century the Swiss botanist A. P. -de Candolle expressed the opinion that trees do not -die from senile decay, but only as the result of injury -or disease. Trees are constructed on a plan fundamentally -different from that underlying the structure -of the highly complex human organism, and are thus -endowed with a sort of potential immortality. It has -been suggested that some of the large corals in the -<span class="pagenum"><a name="Page_8" id="Page_8"> 8 </a></span> -Red Sea which are still tenanted by living polyps -may have been growing in the days of the Pharaohs. -The coral polyp represents the growing portion of a -lifeless mass of rock which is constantly extended by -the activity of the organism at the summit of each -branch. Between a coral-reef and a tree there are -many essential differences, but a rough analogy may -be recognised. A tree, unlike the higher animals, -does not reach a stage at which the whole of its -substance attains a condition of permanence and -fixity. It consists of a complex branching-system -in which each shoot increases in length by virtue -of the youthful vigour of its apex: to a large extent -the tree as a whole consists of lifeless material incapable -of further growth, as is the case of the older -portions of a coral-reef; but the regular increase in -girth of the trunk and its branches demonstrates that -this comparison is only partially true, and that the -power of growth in a tree is not confined to the -extremities of the youngest shoots. The tip of every -twig is composed of minute cells endowed with a -potentiality of development like that which characterises -the embryonic tissues of a seedling just -emerged from the seed. In the course of its growth, -each branch, by means of its living and dividing -cells, contributes to the several parts of the complex -mechanism of the tree. While the greater number -of cells acquire a permanent form and lose the -<span class="pagenum"><a name="Page_9" id="Page_9"> 9 </a></span> -power of further development, there remains a cylinder -of cells endowed with perpetual youth. This -cylinder of living cells, known as the cambium, extends -between the wood and bark from one end of the tree -to the other: by its periodic activity it adds new layers -of tissue each year and thus, by increasing the amount -of conducting tubes for the transport of water and -for the distribution of elaborated food, it enables the -tree to respond to the increasing demands which -are the necessary accompaniment of increasing size. -It has already been pointed out that in the spring -when the sap flows most vigorously the cambial -cylinder produces larger tubes, and afterwards when -the tree settles down to its normal life, these are -succeeded by narrower and stronger tubes. These -later formed elements serve also an important mechanical -purpose; by the strength of their walls they -increase the supporting power of the tree and enable -it to sustain the added burden of the annual increase -in the weight and extent of its spreading branches.</p> - -<p>It is the persistence of permanently juvenile tissue -in certain regions of a tree, together with the remarkable -power of repairing injuries and shedding -effete parts, that constitute some of the most striking -contrasts between the higher animals and plants. -The embryo oak in the earlier stages of development -consists entirely of actively growing cells; by degrees -differentiation of the embryonic tissues results in the -<span class="pagenum"><a name="Page_10" id="Page_10"> 10 </a></span> -localisation of regions of cell-production at the tips -of the elongating stem and root. These apical groups -of cells are, in fact, portions of the embryonic organism -which persist so long as the plant lives. This continuity -between the growing tip of an old oak stem -and the cells of the undifferentiated embryo affords -one of the most remarkable examples in nature of -a link between the past and the present.</p> - -<p>If we pass beyond the stretch of time represented -by the life of a single tree, a few successive generations -suffice to carry our retrospect back to the days -when forests of oaks, birches, and other trees impeded -the progress of the Roman invaders, and, a -stage farther back, to the age of Neolithic man whose -remains are occasionally found in our heaths and -moors and in the submerged forests round our coast. -The blocks of oak and beech, some of which are as -sound as when first felled, recently discovered below -the foundations of parts of Winchester Cathedral constructed -at the end of the twelfth or in the opening -years of the thirteenth century, are relics of Norman -forests. In the course of some excavations at Brigg in -Lincolnshire in 1886 a dug-out boat was found nearly -50 feet long and from 4 to 5 feet in breadth. The stem -of the oak from which the canoe had been fashioned -shows no sign of branching for a length of over 40 -feet, a fact which points to the growth of the tree -in a forest where the race for light induced the -<span class="pagenum"><a name="Page_11" id="Page_11"> 11 </a></span> -development of clean columnar stems. The Brigg -'dug-out,' now in the Hull Museum, was discovered in -an old alluvial valley of the Ancholme river, formerly -connected with the Humber, and it may be that -it was used by Neolithic man as a ferry for river-service(<a href="#Note_7">7</a>).</p> - -<p>From the period claimed by archaeologists we -pass by gradual stages into the domain of the -geologist. As Huxley wrote, 'when even the dim -light of Archaeology fades, there yet remains Palaeontology, -which... has brought to daylight once more -the exuvia of ancient populations, whose world was -not our world, who have been buried in river beds -immemorially dry, or carried by the rush of waters -into caves, inaccessible to inundation since the dawn -of tradition(<a href="#Note_8">8</a>).' The length of time represented by -a succession of long-lived individuals of the same -species becomes enormously extended when we pass -to the history of families, and disinter from the -sediments of other ages the remains of extinct types. -As we descend the geological series familiar types -gradually disappear, and through a succession of -changing floras we penetrate to the fragmentary -records contained in the older rocks until the absence -of documents sets a limit to our quest.</p> - -<p><span class="pagenum"><a name="Page_12" id="Page_12"> 12 </a></span></p> - -<div class="fig_center" style="width: 362px;"> -<a name="Fig_1"></a><img src="images/fig_1.png" width="362" height="293" alt="" /> -<div class="fig_caption">Fig. 1. <i>Pinus sylvestris</i> Linn, in the Black Wood of Rannoch. -(Photograph by Mr A. G. Tansley.)</div> -</div> - -<p>The Scots pine shares with the oak, the beech, -the aspen, the yew, and several other trees the right -to be included in the native flora of Britain. In the -peat-beds of Scotland even up to 3000 feet above -sea-level the stumps of pines occur in abundance, -and in many places recent researches have revealed -the occurrence of successive forests of pines, oaks, -and spruces separated from one another by the -accumulations of swampy vegetation(<a href="#Note_9">9</a>). The spruce -fir has long ceased to be a member of the British -flora, but in a few localities in the Scottish Highlands -patches of primeval pine forests remain. The -<span class="pagenum"><a name="Page_13" id="Page_13"> 13 </a></span> -accompanying photograph (<a href="#Fig_1">Fig. 1</a>), taken by my friend -Mr A. G. Tansley, in the Black Wood of Rannoch in -north-west Perthshire, shows a few trees of <i>Pinus -sylvestris</i> growing in their native soil: the form of -the older tree (<i>A</i>) suggests comparison with that of -a well-grown beech such as we are familiar with -in English plantations. This spreading dome-shaped -habit seems to be a peculiarity of the Highland tree, -and is one of the characters which have led some -botanists to regard it as a variety (<i>Pinus sylvestris</i> -var. <i>scotica</i>) of the ordinary Scots pine. Though it -is doubtful if any relics of primeval pine woods are -left in England, abundant evidence of the former -existence of the Scots pine is afforded by the submerged -forests exposed at low-tide on many parts of -the English and Welsh coasts and at the base of -some of the English peat moors. During the construction -of the Barry docks on the north coast of -the Bristol Channel a few years ago, the exposed -sections of peat and forest beds were investigated by -Dr Strahan and by Mr Clement Reid. There is -evidence of a subsidence of the land to an extent of -55 feet since the formation of the lower peat-beds -containing oak, hazel, willow, and other trees. The -pine, unknown in Wales during the historic period, -was recognised in the Barry cutting. The occurrence -of a polished flint implement assigns a date to the -uppermost portion of this old land-surface(<a href="#Note_10">10</a>).</p> -<p><span class="pagenum"><a name="Page_14" id="Page_14"> 14 </a></span></p> -<p>It is impossible within the limits of a small volume -to discuss in detail the evidence furnished by the -records of the rocks as to the relative antiquity of -the different constituents of the present vegetation -of Britain. In later chapters a few selected plants -are described which are pre-eminently ancient types. -Before passing to the consideration of the data on -which the geological history of plants is based, brief -reference may be made to one of the most interesting -and difficult problems of botanical research, namely -the history of the British flora.</p> -<hr class="chap" /> - -<p><span class="pagenum"><a name="Page_15" id="Page_15"> 15 </a></span></p> - - - -<h2><a name="CHAPTER_II" id="CHAPTER_II">CHAPTER II</a></h2> - -<p class="caption3">THE GEOGRAPHICAL DISTRIBUTION OF PLANTS</p> - -<p class="smaller">'No speculation is idle or fruitless that is not opposed to truth -or to probability, and which, whilst it co-ordinates a body of well -established facts, does so without violence to nature, and with a due -regard to the possible results of future discoveries.' <span class="smcap">Sir Joseph Hooker.</span></p> - - -<p>In the vegetation of the British Isles the leading -<i>rle</i> is played by that large group to which the term -Flowering Plants is frequently applied. This group, -including the two sub-divisions Dicotyledons and -Monocotyledons, is known by the name Angiosperms, -a designation denoting the important fact that the -seeds are developed in an ovary or protective seed-case -(ἁγγειον, a vessel or box). The fact that these -highly elaborated products of development made -their appearance, so far as we know, at a comparatively -late stage in the history of the plant-world, -attests their efficiency as a class and demonstrates -the rapidity with which they have overspread the -surface of the earth as successful competitors in -<span class="pagenum"><a name="Page_16" id="Page_16"> 16 </a></span> -the struggle for existence. As Darwin wrote in a -letter to Sir Joseph Hooker in 1881, 'Nothing is -more extraordinary in the history of the vegetable -kingdom, as it seems to me, than the <i>apparently</i> -very sudden or abrupt development of the higher -plants(<a href="#Note_11">11</a>).' In another letter (1879) to the same friend -we read, 'The rapid development as far as we can -judge of all the higher plants within recent geological -times is an abominable mystery(<a href="#Note_12">12</a>).' Making allowance -for the probability, or indeed certainty, that -the imperfection of the geological record tends to -exaggerate the apparent suddenness of the appearance -of this vigorous class, and allowing for -the fact that our knowledge of the records of -the rocks in which the highest plants first occur -is very incomplete, we cannot escape from the -conclusion that this recently evolved group spread -with amazing rapidity. Various reasons may be -suggested in explanation of the dominant position -which the Angiosperms hold in the floras of the -world. As an instance of their rapid increase during -the Cretaceous epoch<a name="FNanchor_1" id="FNanchor_1"></a><a href="#Footnote_1" class="fnanchor">[1]</a>, the period which has furnished -the earliest satisfactory records of Flowering Plants, -the following statement by an American writer may -be quoted:—'The rapidity with which it [<i>i.e.</i> the -group of Flowering Plants] advanced, conquering or -<span class="pagenum"><a name="Page_17" id="Page_17"> 17 </a></span> -supplanting all rivals, may be better understood -when we remember that it forms 85% of the flora -of the Dakota group '; that is a series of sedimentary -rocks in Dakota referred by geologists to the middle -of the Cretaceous period(<a href="#Note_13">13</a>). In the Wealden rocks -of England, which are rich in the remains of Lower -Cretaceous plants, no undoubted Flowering Plant -has so far been found.</p> - -<div class="footnote"> - -<p><a name="Footnote_1" id="Footnote_1"></a><a href="#FNanchor_1"><span class="label">[1]</span></a> For the position of the Cretaceous and other systems in the -geological series, see the table on <a href="#Page_42">page 42</a>.</p></div> - -<p>The more efficient protection of the ovules, the -germs which, after fertilisation, become the seeds, -the extraordinary variety in the floral mechanisms -for assisting cross-pollination, the arrangements for -nursing the embryo, and the structural features of -the wood in relation both to rapid transport of water -and to the storage of food, are factors which have -probably contributed to the success of the Angiosperms. -The degree of weight to assign to each -contributing cause cannot as yet be satisfactorily -determined, but the general question raised by the -recent origin of these latest products of evolution -offers a promising field for work. While admitting -our inability at present to do more than suggest -possibilities, we may encourage research by speculation.</p> - -<p>The members of the Vegetable Kingdom placed -next to the Flowering Plants are the Gymnosperms -or naked-seeded (γυμνὁς, naked) plants, including -(i) the Conifers, <i>e.g.</i> pines, firs, larches, the yew, etc., -<span class="pagenum"><a name="Page_18" id="Page_18"> 18 </a></span> -(ii) a small group of plants known as the Cycads, -whose existing members, now almost confined to -a few tropical regions, are the descendants of a -vigorous race represented by many species in the -floras of the Mesozoic epoch. A third sub-division -of the Gymnosperms, the Ginkgoales, is represented -by a single survivor, which is described in a later -chapter as one of the most remarkable links with the -past in the plant kingdom.</p> - -<p>The Gymnosperms are geologically very much -older than the Angiosperms. Members of this class -played a prominent part in the vegetation of the -Coal age and it is certain that they existed in the -still older Devonian period. The only other group -to which reference is made in later chapters is that -of the Ferns, one of the sub-divisions of a large class -known as the Vascular Cryptogams or Pteridophyta. -These plants, like the Gymnosperms, are represented -in the oldest floras of which recognisable remains -have been preserved. The main groups of the -vegetable kingdom, founded on existing plants, are -distinguished by well-defined differences; they are -comparable with separate twigs of a tree springing -from larger branches and these again uniting below -in a common trunk. The vegetation of to-day represents -only the terminal portions of the upper -branches. As we descend the geological series, -records of extinct types are found which enable -<span class="pagenum"><a name="Page_19" id="Page_19"> 19 </a></span> -us either to trace the separate branches to a common -origin or to recognise a convergence towards a -common stock. Were a botanist to find himself in -a forest of the Coal age he would experience great -difficulty in assigning some of the plants to their -systematic position: characters now regarded as -distinguishing features of distinct groups would be -met with in combination in a single individual. It -is by the discovery of such generalised types, which -serve as finger-posts pointing the way to lines of -evolution, that the student of pre-existing plants has -been able to throw light on the relative antiquity of -existing forms, and to trace towards a common -ancestry plants which now show but little indication -of consanguinity.</p> - -<p>Confining our attention to the dominant group of -plants in the British flora, namely the Flowering -Plants, we may profitably consider the question, -though we cannot satisfactorily answer it,—which -members of this group are entitled to be regarded -as the most ancient inhabitants? The past history -of our native plants, and their geographical range, -not only in the British Isles but on the Continent -of Europe, are subjects well worthy of the attention -of field-botanists whose interests are apt to be -confined within too narrow bounds. There are -numerous problems relating to the composition of -the present vegetation of Britain which might be -<span class="pagenum"><a name="Page_20" id="Page_20"> 20 </a></span> -discussed in reference to the relative antiquity of -plants; but in a single chapter it is impossible to do -more than call attention to certain considerations -which are frequently overlooked by students of -British species.</p> - -<p>It is customary to speak of the British flora as -consisting for the most part of species introduced -into this country by natural means, while some -plants owe their introduction to human agency or -are 'escapes' from cultivation. It is by no means -an easy task in some instances to decide whether a -species is native or introduced, but in some cases, -a few of which are mentioned, there is no doubt as to -the alien nature of the plants. The term 'native' -needs a word of explanation. It is not intended to -convey the idea that a plant so designated came into -existence on British soil and spread thence to other -regions; but by native species we mean such as have -reached this country by migration from other lands, -or it may be in some instances have actually originated -in this part of Europe. One of the best known -aliens in Britain is the American water-weed, <i>Elodea -canadensis</i> (or <i>Anacharis alsinastrum</i>), which was -discovered about sixty years ago in a canal near -Market Harborough in Leicestershire(<a href="#Note_14">14</a>). In all probability -this North American species was introduced -into England with timber. Once established, it -spread through the waterways with alarming rapidity -<span class="pagenum"><a name="Page_21" id="Page_21"> 21 </a></span> -and became a serious pest. Elodea affords an admirable -instance of the serious interference with the -balance of Nature by the introduction of a new -competitor into an environment conducive to -vigorous development. Another foreign water-plant, -<i>Naias graminea</i>, for the importation of which -Egyptian cotton may be responsible, has been -recorded from the Reddish canal near Manchester(<a href="#Note_15">15</a>). -This African and Asiatic species occurs in Europe only -as a colonist; it is said to have been introduced into -Italy with East Indian rice. A more recent case of alien -immigration due to unintentional human agency is -that of <i>Potamogeton pennsylvanicus</i>, a pond-weed of -Canada, the United States, Jamaica, and elsewhere. -Specimens of this species were first noticed in 1907 -in a canal near Halifax close to the effluent from -a cotton mill. Since its discovery the plant has -slightly extended its range. It is suggested by -Mr Bennett, who first identified the alien, that its -fruits were brought to this country in goods from -the United States(<a href="#Note_16">16</a>).</p> - -<p>Of the introduction of these and other foreign -plants we have satisfactory records; but there are -many others which may owe their presence to man's -agency, though we have no information as to their -arrival.</p> - -<p>It has long been recognised that several members -of the British flora are related to Scandinavian -<span class="pagenum"><a name="Page_22" id="Page_22"> 22 </a></span> -species. The Scandinavian flora, as Sir Joseph -Hooker says in his well-known paper on the 'Outlines -of the Distribution of Arctic plants,' 'not only -girdles the globe in the Arctic Circle, and dominates -over all others in the North Temperate Zone of the -Old World, but intrudes conspicuously into every -other temperate flora, whether in the northern or -southern hemisphere, or on the Alps of tropical -countries'(<a href="#Note_17">17</a>). The view generally held is that during -the Glacial period this Arctic flora was driven -South, and aided by land-bridges, which were afterwards -submerged, many of the northern migrants -found a more congenial home in Britain. It is however -by no means improbable that this conclusion -may have to be considerably modified. Mr and Mrs -Reid, as the result of their careful analysis of the -Pre-Glacial Flora of Britain, express the opinion that -'the pre-glacial plants suggest climatic conditions -almost identical with those now existing, though -slightly warmer' (27, 2). It is noteworthy that the -list of plants given in their paper does not include -any typical Arctic species. The occurrence on the -mountains of Scotland and elsewhere of such plants as -<i>Silene acaulis</i>, <i>Dryas octopetala</i>, <i>Saxifraga oppositifolia</i> -and other Saxifrages, <i>Rubus chamaemorus</i> (the -Cloudberry), and the dwarf Birch illustrate the Arctic-Alpine -element in our flora.</p> - -<p>The opinion is held by many Swiss botanists that -<span class="pagenum"><a name="Page_23" id="Page_23"> 23 </a></span> -their Alpine species have in large measure been -derived from non-glaciated parts of the Pyrenees, that -is from a region which was presumably able to retain -its flora at a time when more northern lands were -exposed to extreme Arctic conditions. My friend -Dr Moss believes that some of the so-called Scandinavian -plants came to Britain from Central Europe -after the retreat of the ice; if this view is correct it -means that some at least of our Arctic-Alpine plants -reached these islands by a southern rather than by -a northern route.</p> - -<p>Interesting examples of far-travelled northern -plants recently described by Professor Engler of -Berlin afford additional illustrations of the general -principles enunciated many years ago by Sir Joseph -Hooker. A species of flowering Rush, <i>Luzula -spicata</i> var. <i>simensis</i>, occurs at an altitude of 3600 -metres in Abyssinia and on Kilimanjaro. <i>Luzula -spicata</i> is found in the whole of the Arctic and -Subarctic belt in Scotland, Auvergne, the Jura -mountains, and elsewhere. The species probably -began its career in the northern hemisphere where -it grew abundantly on the higher ground in the -Arctic Circle: it eventually travelled along the -North American Andes and appeared in Mexico -under a guise sufficiently distinct to warrant the -use of another name, <i>Luzula racemosa</i>. In an -eastern direction it reached the Himalayas and is -<span class="pagenum"><a name="Page_24" id="Page_24"> 24 </a></span> -represented in Abyssinia by a closely allied form. -From Abyssinia to Kilimanjaro <i>Luzula spicata</i> 'had -to travel a long distance; but it is not impossible -that it either still exists or has existed previously -on a few of the high mountains between Abyssinia -and Kenia, from which, having advanced to the -Kilimanjaro, it again produced new forms.... At any -rate, it is impossible to do without distribution of -seeds of alpine plants by air-currents or by birds -from one mountain to the other in explaining the -history of distribution'(<a href="#Note_18">18</a>).</p> - -<p>The majority of British plants are identical with -species in Central and Northern Europe: of these, -some are among the most widely spread English -species, <i>e.g.</i> the Daisy and Primrose, while others, -such as the Oxlip (<i>Primula elatior</i>), are confined to -the Eastern counties, and others, such as the Cheddar -Pink (<i>Dianthus caesius</i>), are restricted to Western -counties.</p> - -<p>Before considering a small section of the British -flora which is the most interesting from the point of -view of origin, a short digression may be allowed in -order to call attention to the importance of a branch -of science which Darwin spoke of as 'that grand -subject, that almost keystone of the laws of creation, -geographical distribution,' and in 1847 referred to -as 'that noble subject of which we as yet but dimly -see the full bearing.' It was largely as the results -<span class="pagenum"><a name="Page_25" id="Page_25"> 25 </a></span> -of his study of distribution in the Galapagos Islands -that Darwin determined to 'collect blindly every -sort of fact which bears anyway on what are species.' -The acceptance of the view 'that each species was -first produced within a single region'(<a href="#Note_19">19</a>), raises the -subject of geographical distribution to a far higher -plane than it occupied in pre-Darwinian days. Although -most people are familiar with some of the -commoner means by which plants are able to colonise -new ground through the adaptation of their fruits and -seeds to various methods of transport, the conception -of a plant as a stationary organism tends to prevent -due allowance being made for the comparative -facility with which, in the course of successive -generations, a species is able to wander from place -to place. The individual animal is endowed with -powers of locomotion enabling it to seek new feeding-grounds -and to avoid enemies; but with the -exception of some of the simplest forms a plant -cannot move—'le matin la laisse o la trouve le -soir.'</p> - -<p>The rate of travel may or may not be rapid, but -in a comparatively short time, if the conditions are -favourable, a tree may spread over a wide area. -Mr Ridley, Director of the Botanic Gardens, Singapore, -writes as follows in reference to the rate of -travel of one of the common Malayan trees (<i>Shorea -leprosula</i>), which bears winged fruits particularly -<span class="pagenum"><a name="Page_26" id="Page_26"> 26 </a></span> -well adapted to wind-transport: 'If we assume that a -tree flowers and fruits at 30 years of age and the fruits -are disseminated to a distance of 100 yards, that the -furthest fruits always germinate and so continue in -one direction, it will be seen that under such most -favourable circumstances the species can only spread -800 yards in 100 years, and would take 58,666 years -to migrate 100 miles'(<a href="#Note_20">20</a>).</p> - -<p>There is, however, one type of distribution—what -is called discontinuous distribution—to which -special attention should be directed on account of its -intimate association with questions relating to the -past history of living organisms. Many examples -might be quoted from both the animal and plant -kingdoms in support of the view that discontinuous -distribution is a criterion of antiquity. When identical -or very nearly identical plants occur in regions -separated from one another by areas in which the -particular species is unknown, the inference is either -that the surviving individuals are remnants of a large -number formerly distributed over a wider continuous -area, or that in the course of evolution similar conditions -in widely separated areas led to the production -of identical types. The former view is much the more -probable: it is consistent with the conclusions arrived -at on other grounds as to the connexion between -discontinuous distribution and ancient lineage. The -explanations of the widespread occurrence among -<span class="pagenum"><a name="Page_27" id="Page_27"> 27 </a></span> -different races of similar objects or legends afford an -analogous case. As Dr Andrew Lang points out in -<i>Custom and Myth</i>, it is held by some students that -the use of the bull roarer—to cite a specific instance—by -different peoples denotes descent from a common -stock, though he considers the more probable explanation -to be that similar minds, working with -simple means towards similar ends, might evolve the -bull roarer and its mystic uses anywhere.</p> - -<p>The Cedars of Lebanon afford an interesting example -of discontinuous distribution. They illustrate -how a species, which may be assumed to have -originated in one region, in the course of its -wanderings may undergo slight changes until, at -a later stage when the plants have disappeared from -parts of the once-continuous area, the remaining -outlying groups of individuals are spoken of under -different specific names. The cedars of Lebanon, -known as <i>Cedrus libani</i>, occur as isolated groups -on the Lebanon hills as outliers of the larger forests -of the Taunus 250 miles distant. The African cedar, -<i>Cedrus atlantica</i>, is separated from the Lebanon -cedar by a distance of 1400 miles. Approximately -the same distance divides the Lebanon cedar from -the deodar, <i>Cedrus deodara</i>, which extends from -Afghanistan along the Himalayas almost to the -confines of Nepal. Sir Joseph Hooker regards the -three cedars as varieties of one species which once -<span class="pagenum"><a name="Page_28" id="Page_28"> 28 </a></span> -formed a continuous forest: he attributes the present -discontinuous distribution, in part at least, to the -effects of a warmer succeeding a colder climate. The -less favourable conditions drove the vegetation of -the lowlands to seek more congenial habitats at -higher altitudes. In this connexion it is interesting -to find that in Algeria the cedar is confined to the -higher ground where the snow lies long in the -spring(<a href="#Note_21">21</a>).</p> - -<p>The Tulip Tree of North America and Central -China affords one of many examples of existing -flowering plants which illustrate the close connexion -between present distribution and past history. The -genus Liriodendron, often cultivated in the south -of England, is now represented by two species, the -best known of which—the Tulip Tree, <i>Liriodendron -tulipera</i>—extends from Vermont to Florida and -westwards to Lake Michigan and Arkansas. The -leaves bear a superficial resemblance to those of -the Sycamore, but are as a rule easily distinguished -by the truncated form of the apex; the specific name -was suggested by the tulip-like form of the flowers. -Fossil leaves of Liriodendron are not uncommon in -the Cretaceous rocks of Disco Island in latitude 70° N., -where they occur with other flowering plants which -bear striking testimony to the mildness of the Cretaceous -climate in high northern latitudes. One -of the associated flowering plants is a species of -<span class="pagenum"><a name="Page_29" id="Page_29"> 29 </a></span> -Artocarpus, described by Dr Nathorst as <i>Artocarpus -Dicksoni</i> which bears a close resemblance to <i>A. incisa</i> -the bread-fruit tree of the southern tropics of the -Old World. Without attempting to deal fully with -the past history of Liriodendron, it may be confidently -stated that the records of the rocks are consistent -with the idea of antiquity suggested by the present -distribution of the two surviving species.</p> - -<p>Islands such as Great Britain and Ireland, situated -a short distance from a continent, contain many plants -which are widely spread in different parts of the -world, together with a very small number peculiar -to the British Isles though closely allied to species -on the neighbouring continent or to plants farther -afield. The occasional recognition of species previously -believed to be confined to Britain tends to -reduce the short list of our endemic types.</p> - -<p>An enquiry into the origin of an island flora -involves a consideration of the data in regard to -changes in level and relative distribution of land -and water in the course of geological evolution. It -is generally agreed that at no distant date, in a -geological sense. Great Britain and Ireland were -united to the continent. There is, however, another -fact to reckon with, namely the prevalence of Arctic -conditions in northern Europe when a thick sheet of -ice spread over the greater part of the British Isles. -There can be no doubt that the severity of the climate -<span class="pagenum"><a name="Page_30" id="Page_30"> 30 </a></span> -during the Glacial period was such as to destroy -a large proportion of the vegetation. The question -is, were all the flowering plants destroyed or were -some of the hardier species able to survive, either on -the higher peaks which kept their heads above the -level of the ice or on the southern fringe of England -beyond the ice-covered region? It is impossible to -give a definite answer: the probability is that nearly -all the pre-Glacial species were destroyed, but it is -not impossible that some Alpine-Arctic plants escaped -extinction, while others retreated to more southern -and less Arctic areas by means of a land-connexion -with France or crossed the intervening sea by ocean-currents, -by animal agency, or by wind.</p> - -<p>Although we possess but imperfect information as -to the extent and duration of land-bridges between -Britain and the continent, there are no special -difficulties in the way of accounting for the presence -of Scandinavian, Germanic, and other elements in the -British flora. There are, however, other and more -difficult problems to consider in reference to a small -group of flowering plants which are met with in the -west and south of Ireland, also, to a less extent, in -Cornwall and in a few other localities in the south-west -of England. In Connemara in the west of Ireland, -where hard frosts are unknown and winter snows are -rare, there are three kinds of Heath, St Dabeoc's Heath -(<i>Daboecia polifolia</i>), the Mediterranean Heath (<i>Erica -<span class="pagenum"><a name="Page_31" id="Page_31"> 31 </a></span> -mediterranea</i>) and <i>Erica Mackaii</i> which are not -found elsewhere in the British Isles or in the whole -of northern Europe, but reappear in the Pyrenees. -The London Pride (<i>Saxifraga umbrosa</i>), another -Pyrenean plant, grows on the south and west coast -of Ireland from Waterford to Donegal. <i>Arbutus -Unedo</i>, the Strawberry tree, which flourishes in the -Killarney district of County Kerry and occurs in -neighbouring localities, has a wide distribution in -the Mediterranean region. Devonshire and Cornwall -possess two other Heaths, <i>Erica ciliaris</i>, which extends -into Dorsetshire and occurs in north Brittany, -and <i>Erica vagans</i>, both Pyrenean species, while a -Mediterranean plant. <i>Gladiolus illyricus</i>, grows in the -New Forest.</p> - -<p>In 1846 Edward Forbes dealt with the problems -presented by the distribution of British plants in an -essay which has exercised a far-reaching influence. -When Forbes published his work, comparatively little -was known as to the possibilities of transport of seeds -and fruits across barriers of water(<a href="#Note_22">22</a>). His conviction -that the known means of dispersal were insufficient -to account for the presence of Mediterranean or -Lusitanian plants in Ireland led him to turn to -geology for a solution of the problem. He was thus -led to put forward the view that in the course of -the Tertiary period when, as we know from palaeontological -evidence, the climate of north and west -<span class="pagenum"><a name="Page_32" id="Page_32"> 32 </a></span> -Europe was much warmer than it is now, and long-before -the beginning of the climatic changes which -culminated in the Glacial period, there was a land-connexion -between the west of Ireland and the -south-west of the continent. Mr Praeger, whose -work on the Irish flora is well known to systematic -botanists, agrees with the conclusions of Forbes, and -sees in the Portuguese and Mediterranean plants -'relics of a vegetation which once spread along a -bygone European coast-line which stretched unbroken -from Ireland to Spain'(<a href="#Note_23">23</a>). If this explanation is -correct it entitles Arbutus, St Dabeoc's heath and -other members of this southern group to be regarded -as a very old section of our flora. There is, however, -another side to the question: granting that a certain -number of Irish plants were able to withstand the -rigours of an Ice age, it is hardly likely that the -strawberry tree and other southern types, which it -is admitted flourish in the south-west of Ireland -because of the mildness of the climate, were of the -number of those which endured an extreme Arctic -phase. Moreover, if these Mediterranean species are -survivals from the Tertiary period, if they have been -isolated since pre-Glacial days as an outlier of a -southern flora, we might fairly expect that during -the long interval between their arrival and the -present day new forms would have been produced -closely related to, though not identical with, the -<span class="pagenum"><a name="Page_33" id="Page_33"> 33 </a></span> -parent types. This, however, has not been proved to -be the case. Darwin in speaking of Forbes' Essay in -a letter to de Candolle in 1863 says that he differs -from most of his contemporaries 'in thinking that -the vast continental extensions of Forbes, Heer, and -others are not only advanced without sufficient evidence, -but are opposed to much weighty evidence'(<a href="#Note_12">12</a>). -The alternative view is to regard Arbutus and its -compatriots as post-Glacial arrivals and not as survivals -from a widely spread Tertiary flora.</p> - -<p>A recently published account of the New Flora -of the volcanic island of Krakatau furnishes an -instructive and remarkable demonstration of the -facility with which a completely sterilised island, -separated by several miles of ocean from neighbouring -lands, may be restocked with vegetation(<a href="#Note_24">24</a>). -In 1883 the island of Krakatau, then densely covered -with a luxuriant tropical vegetation, was partially -destroyed by a series of exceptionally violent volcanic -explosions. After this catastrophe only a third of -the island was left: the surface was deeply covered -by pumice and volcanic ash and no vestige of life -remained. In 1906 a party of botanists who spent -a few hours on Krakatau collected 137 species of -plants: the vegetation was in places so dense that -it was with the greatest difficulty they penetrated -beyond the coastal belt, and some of the trees had -reached a height of 50 feet. The seeds and fruits -<span class="pagenum"><a name="Page_34" id="Page_34"> 34 </a></span> -of this new flora have been carried by ocean-currents, -by wind, and by the agency of birds from other -islands in the Malay Archipelago. The nearest -islands, except the small island of Sebesi, about -12 miles distant, are Java and Sumatra, separated -from Krakatau by a stretch of water about 25 miles -in breadth. It is reasonable to wonder whether, had -Forbes known of this and similar modern instances -of the capabilities of plants as travellers, he would -have adopted the view he did. In this connexion it -may be added that in recent years the glaciation of -Ireland has been shown to be more extensive than it -was believed to be when Forbes wrote his essay.</p> - -<p>There would seem to be no insuperable objection -to the conclusion that the Mediterranean plants in -Ireland and in the south of England reached their -present home after the retreat of the ice at the -end of the Glacial period, and after Ireland became -an island. A full consideration of the problem is -beyond the scope of this book, but I have briefly -stated the case, not with the authority of an expert -but in order to draw attention to a particularly -fascinating study in plant-migration.</p> - -<p><span class="pagenum"><a name="Page_35" id="Page_35"> 35 </a></span></p> - -<div class="fig_center" style="width: 359px;"> -<a name="Fig_2"></a> -<img src="images/fig_2.png" width="359" height="460" alt="" /> -<div class="fig_caption">Fig. 2. <i>Eriocaulon septangulare</i> With. West Connemara. -(Photograph by Mr W. R. Welch.)</div> -</div> - -<p><span class="pagenum"><a name="Page_36" id="Page_36"> 36 </a></span></p> - -<p>In a volume by W. Canton entitled <i>A Child's -book of Saints</i> a story is told in which the presence -in Ireland of Mediterranean species receives a more -picturesque explanation. The Monk Bresal was sent -to teach the brethren in a Spanish monastery the -music of Irish choirs. In later years Bresal longed -for a sight of his native land, though he loved his -home and 'every rock, tree, and flower' in his adopted -country. After returning to Ireland, his thoughts -reverted to Spain; 'it appeared to him as though -he was once again in a granite nook among the rocks -beside the Priory'; he saw the ice-plant with its -little stars of white flowers sprinkled with red (the -London Pride) and a small evergreen tree from which -he had often gathered the orange-scarlet berries -(Arbutus). The Prior of the Spanish monastery 'with -heavenly vision saw Bresal gazing at the evergreen -tree and the ice-plant, and turning to the trees -blessed them and commended them to go and make -real his dream. As Bresal brushed away his tears -he saw with amazement at his feet the ice-plant and -hard by the evergreen tree.'</p> - -<p>The plant represented in (<a href="#Fig_2">Fig. 2</a>) is another -British species which tasks the ingenuity of students -of plant-geography. This is the Pipe Wort (<i>Eriocaulon -septangulare</i>), the sole representative in -Europe of a certain family of Monocotyledons: it -flourishes in the west of Ireland and in the western -islands of Scotland but nowhere else in Europe; it is -native on the other side of the Atlantic in Canada -and the northern United States of America. Mr -Praeger in describing the striking mixture of species -in the west of Ireland writes, 'The pool from which -<span class="pagenum"><a name="Page_37" id="Page_37"> 37 </a></span> -we gather the American Pipe Wort is fringed with -Pyrenean Heathers. The cracks which are filled with -the delicate green foam of the maiden hair are set in -Bearberry and Spring Gentian; <i>Habenaria intacta</i>, -far from its Mediterranean home, sends up its flower-spikes -through carpets of mountain Avens; and -St Dabeoc's Heath and the dwarf Juniper straggle -together over the rocky knolls'(<a href="#Note_25">25</a>).</p> - -<p>The presence of Eriocaulon on the western edge -of Europe may be attributed to migration in pre-Glacial -days from North America by way of a land-connexion, -of which Greenland and Iceland represent -surviving portions. The opinion held by Forbes, and -advocated by some later naturalists, that the southern -companions of Eriocaulon in the west of Ireland are -survivors from a Tertiary flora which have lived -through the Ice Age, is consistently extended to the -Pipe Wort. On the other hand, before yielding to -the temptation to regard these American and Mediterranean -species as links with the Tertiary period, -we must be convinced that the possibilities of -post-Glacial introduction, even without the aid of -land-bridges, have been exhausted. The Pipe Wort -is a botanical puzzle which affords a good example of -the accession of interest to field-botany effected by a -knowledge of the distribution of the component -members of the British flora. The problem of its -past history suggests an experimental enquiry into -<span class="pagenum"><a name="Page_38" id="Page_38"> 38 </a></span> -the adaptability of its seeds to dispersal, and emphasises -the importance of the co-operation of -botanists and geologists in a common endeavour to -trace the origin of British plants.</p> - -<p>In addition to the Pipe Wort, mention may be -made of three other American flowering plants -recognised in the Irish flora. <i>Sisyrinchium angustifolium</i> -recorded from the west of Ireland is native -in temperate North America; the orchid, <i>Spiranthes -romanzoffiana</i>, met with in the south and north of -Ireland, is widely spread in Canada and the northern -States, while <i>Sisyrinchium californicum</i>, a native -of California and Oregon, was discovered by Mr Marshall -in marshy meadow-land near Wexford(<a href="#Note_26">26</a>). In -the case of the more recently discovered American -immigrants, the possibility of human introduction -must be borne in mind, though there are no special -reasons for doubting that some, as in the case of Eriocaulon, -reached the Irish coast by natural agencies.</p> -<hr class="chap" /> - -<p><span class="pagenum"><a name="Page_39" id="Page_39"> 39 </a></span></p> - - - -<h2><a name="CHAPTER_III" id="CHAPTER_III">CHAPTER III</a></h2> - -<p class="caption3">THE GEOLOGICAL RECORD</p> - -<p class="smaller">'All the Epochs of the Past are only a few of the front carriages, -and probably the least wonderful, in the van of an interminable -procession.' <span class="smcap">J. B. Bury</span> (<i>The Science of History</i>).</p> - - -<p>The portion of the earth's surface accessible to -investigation is made up in part of accumulations -of old sediments, some indistinguishable from the -shingle, sand, and mud now in process of formation -by the ceaseless action of denudation; others have -been hardened, gently folded or violently contorted -and so far altered by crust-movements as to render -their sedimentary origin well nigh unrecognisable. -It is these sediments of former ages, the dust of lost -continents, in which are preserved the majority of -the fragmentary remains of plants and animals, the -flotsam and jetsam of successive phases of evolution.</p> - -<p>The crust of the earth, as Darwin wrote, 'with its -imbedded remains must not be looked at as a well -filled museum, but as a poor collection made at -hazard and at rare intervals'(<a href="#Note_19">19</a>). It is from this -<span class="pagenum"><a name="Page_40" id="Page_40"> 40 </a></span> -imperfect record that we seek to discover the relative -antiquity of the several groups or genera of living -plants, and in the structure of extinct types we -endeavour to discover connecting links between -divisions of the plant kingdom which in the course -of evolution have retained little or no signs of a -common descent.</p> - -<p>Sir Joseph Hooker in a letter to Darwin in 1859 -speaks of his 'conviction that we have not in a -fossilised condition a fraction of the plants that have -existed, and that not a fraction of those we have are -recognisable specifically'(<a href="#Note_12">12</a>). Considering the nature -of the palaeontological documents the wonder is how -much they have taught us, and we may look with -confidence to the results of future research in a field -of which the importance has only recently been -appreciated. With the strata of sedimentary origin -are frequently associated igneous rocks, and in many -continental regions, as in the majority of oceanic -islands, the crust of the earth consists wholly of -volcanic material or of rocks produced by the gradual -solidification of molten magmas. Rocks composed -mainly of carbonate of lime, such as limestones and -chalk, bear witness to ocean beds or to sediments -deposited on the floors of inland seas beyond the -reach of land detritus where coral reefs were reared -or the shells and other calcareous skeletons of -animals supplied the material for future land. In -<span class="pagenum"><a name="Page_41" id="Page_41"> 41 </a></span> -such rocks the remains of calcareous seaweeds are -frequently recognisable and occasionally, as in the -English chalk, fragments of wood testify to transport -from a distant land.</p> - -<p>While there is little difficulty in explaining the -nature of much of the earth's crust, in several parts of -the world the strata are totally unfossiliferous and -closely simulate crystalline rocks. In many cases -it is believed that such strata represent ancient -sediments which in the course of ages have been -reduced by metamorphic agencies to a condition -which has obscured or entirely obliterated all traces -of their pristine state.</p> - -<p>Since the pioneer work of William Smith, who -in the early days of the nineteenth century first -realised the importance of fossils as aids to the -determination of relative age, geologists have devoted -themselves to the task of correlating the sedimentary -rocks of the world, using as criteria the order of -superposition of the strata and the nature of their -organic remains. The result has been to classify -portions of the earth's crust into periods or chapters, -which together constitute a record of geological -evolution as complete as it is possible to obtain from -the available data. The accompanying table shows -the order of sequence of the epochs, which stand for -terms of years of a magnitude beyond our powers to -grasp.</p> - -<p><span class="pagenum"><a name="Page_42" id="Page_42"> 42 </a></span></p> - -<p>The division of geological history into larger and -smaller periods does not imply the recurrence of -sudden revolutions; it is in some measure dictated -by considerations of convenience, but more particularly -by our ignorance of certain stages in the -history of the world due to the imperfection of the -record.</p> - - -<p class="caption3">GEOLOGICAL TABLE.</p> - -<p class="center">Showing the position in the Geological Series of the strata referred -to in this volume.</p> - -<table style="width: 35em; margin: 2em auto;" summary="Series"> -<tr> - <td colspan="5"><span class="smcap caption3nb">Tertiary (Cainozoic)</span></td> -</tr> -<tr> - <td rowspan="5"> </td> - <td rowspan="5"><img src="images/bracel_160.png" width="11" height="160" alt="{" /></td> - <td><b>Recent</b><br /> - <b>Pleistocene</b></td> - <td><img src="images/bracel_60.png" width="11" height="60" alt="{" /></td> - <td><p class="hanging">Superficial accumulations containing human remains (Metal age, - Neolithic and Palaeolithic ages, Glacial deposits)</p></td> -</tr> -<tr> - <td><b>Pliocene</b></td> - <td></td> - <td class="tdl">Cromer Forest-bed, etc.</td> -</tr> -<tr> - <td><b>Miocene</b></td> - <td></td> - <td class="tdl">Absent from Britain.</td> -</tr> -<tr> - <td><b>Oligocene</b></td> - <td></td> - <td class="tdl">Bovey Tracey beds, etc.</td> -</tr> -<tr> - <td><b>Eocene</b></td> - <td></td> - <td class="tdl">London Clay, etc.</td> -</tr> -<tr> - <td colspan="5"><span class="smcap caption3nb">Secondary (Mesozoic)</span></td> -</tr> -<tr> - <td rowspan="3"> </td> - <td rowspan="3"><img src="images/bracel_160.png" width="11" height="160" alt="{" /></td> - <td><b>Cretaceous</b></td> - <td><img src="images/bracel_32.png" width="11" height="32" alt="{" /></td> - <td class="tdl">Chalk<br /> - Wealden beds</td> -</tr> -<tr> - <td><b>Jurassic</b></td> - <td><img src="images/bracel_60.png" width="11" height="60" alt="{" /></td> - <td class="tdl">Purbeck and Portland beds (Upper Jurassic)<br /> - Oolites (Middle Jurassic)<br /> - Lias (Lower Jurassic)</td> -</tr> -<tr> - <td><b>Triassic</b></td> - <td><img src="images/bracel_60.png" width="11" height="60" alt="{" /></td> - <td class="tdl">Rhaetic beds<br /> - Keuper " (Marls with rock-salt, etc.)<br /> - Bunter "</td> -</tr> -<tr> - <td colspan="5"><span class="smcap caption3nb">Primary (Palaeozoic)</span><br /> - <span class="pagenum"><a name="Page_43" id="Page_43"> 43 </a></span></td> -</tr> -<tr> - <td rowspan="7"> </td> - <td rowspan="7"><img src="images/bracel_320.png" width="11" height="320" alt="{" /></td> - <td><b>Permian</b></td> - <td><img src="images/bracel_60.png" width="11" height="60" alt="{" /></td> - <td class="tdl">Red Sandstones, etc.<br /> - Magnesian limestone</td> -</tr> -<tr> - <td class="tdl"><b>Carboniferous</b></td> - <td><img src="images/bracel_60.png" width="11" height="60" alt="{" /></td> - <td class="tdl">Coal Measures<br /> - Millstone Grit<br /> - Carboniferous limestone</td> -</tr> -<tr> - <td><b>Devonian</b></td> - <td><img src="images/bracel_32.png" width="11" height="32" alt="{" /></td> - <td class="tdl">Devonian limestones, etc.<br /> - Old Red Sandstones</td> -</tr> -<tr> - <td><b>Silurian</b></td> - <td></td> - <td class="tdl">Sandstones, shales, some limestone</td> -</tr> -<tr> - <td><b>Ordovician</b></td> - <td><img src="images/bracel_32.png" width="11" height="32" alt="{" /></td> - <td class="tdl">Slates, sandstones,<br /> - Volcanic rocks, etc.</td> -</tr> -<tr> - <td><b>Cambrian</b></td> - <td></td> - <td class="tdl">Slates, Sandstones, etc.</td> -</tr> -<tr> - <td><b>Pre-Cambrian</b><br /> <b>or Archean</b></td> - <td><img src="images/bracer_32.png" width="11" height="32" alt="{" /></td> - <td class="tdl">Slates, Volcanic rocks, etc.</td> -</tr> -</table> - - -<p>In certain parts of the world, as for example the -north-west Highlands of Scotland, the Malvern Hills, -Scandinavia, and in many other regions in Europe -and North America, geologists have recognised what -they believe to be the foundation stones of the -world. These Archaean rocks, which underlie the -oldest fossiliferous strata, belong to a period of -geological evolution from which it appears to be -hopeless to obtain any light as to the nature of the -contemporary organic world. The earliest vestiges of -life so far discovered exhibit a high degree of organisation, -which unmistakably points to their being links in -a chain extending far beyond the limits of the oldest -<span class="pagenum"><a name="Page_44" id="Page_44"> 44 </a></span> -Cambrian strata in which recognisable fossils first -occur. The rocks of the Cambrian and Ordovician -epochs, as represented by the grits, shales, slates -and other sedimentary strata in Wales, Shropshire, the -Lake district and elsewhere, though in places rich in -the remains of animals, afford no information in regard -to the land vegetation. From the succeeding Silurian -epoch very little evidence has been gleaned as to the -nature of the flora, and it is not until we come to the -sedimentary rocks of the Devonian era that records -of plant-life occur in any abundance. The almost -complete lack of botanical data in the pre-Devonian -formations is in part due to the fact that these older -rocks consist to a large extent of marine deposits -formed under conditions unfavourable to the preservation -of plants. That the land-surfaces of the older -Palaeozoic eras supported an abundant vegetation -there can be little doubt. The relics of plant-life -furnished by the Devonian and succeeding formations -represent the upper branching-systems of a deeply -rooted and spreading tree, the lowest portions of -which have been destroyed or have left no sign of -their existence.</p> - -<p>In descending the Geological series, we begin with -superficial deposits, such as peat and river-gravels -found subsequently to the underlying boulder-clay of -the Glacial period. The remains of forest trees preserved -in the peat and in submerged forests round -<span class="pagenum"><a name="Page_45" id="Page_45"> 45 </a></span> -the coast connect the vegetation of the historic period -with that of the Neolithic age. At the base of the -Pleistocene series, the name given to the latest -chapter of geological history, we find evidence of the -prevalence of arctic conditions in the widely spread -boulder-clays and other deposits of the Glacial period.</p> - -<p>From deposits of post-Glacial date abundant plant -remains have been obtained, but we cannot say with -any degree of certainty what proportion of these -plants remained in Britain during the Ice age, and -whether the greater part of the vegetation, the relics -of which have been discovered in pre-Glacial beds, -was destroyed or driven south by the advancing ice. -We may briefly consider some of the more interesting -facts brought to light by the investigation of the -fossil plants in the Lower Pleistocene and Upper -Tertiary beds. It is mainly to the researches of -Mr Clement Reid into the vegetation of Britain -immediately preceding the Glacial period, that our -knowledge of this phase of the history of the British -flora is due.</p> - -<p><span class="pagenum"><a name="Page_46" id="Page_46"> 46 </a></span></p> - -<div class="fig_center" style="width: 377px;"> -<a name="Fig_3"></a> -<img src="images/fig_3.png" width="377" height="395" alt="" /> -<div class="fig_caption">Fig. 3. Pre-Glacial plants from Mundesley (A), Norfolk and Pakefield -(B, C), Suffolk. (Photographs by Mr Clement Reid and Mrs -E. M. Reid.) A. <i>Bidens tripartita</i> Linn. (× 6); B. <i>Picea excelsa</i> -Linn. (nat. size). C. <i>Stellaria holostea</i> Linn. (× 12).</div> -</div> - -<p>On the coast of Norfolk in the neighbourhood of -Cromer the sections of the cliffs reveal the existence -of a succession of sands, clays, and gravels underlying -Glacial deposits; this material was probably laid -down near the mouth of the ancient Rhine, which in -the latter part of the Tertiary period flowed across -a low area, which is now occupied by the shallow -southern half of the North Sea(<a href="#Note_27">27</a>). The plant-fragments -found in these river-sediments indicate a -<span class="pagenum"><a name="Page_47" id="Page_47"> 47 </a></span> -temperate climate. Among the plants of this pre-Glacial -flora are many familiar British species, such as -<i>Caltha palustris</i> (marsh marigold), species of butter-cup, -<i>Stellaria holostea</i> (greater stichwort) (<a href="#Fig_3">Fig. 3, C</a>), -<i>Bidens tripartita</i> (bur-marigold) (<a href="#Fig_3">Fig. 3, A</a>), maple, -hawthorn, the alder, hazel, the yew, Scots pine and -numerous others. If, as is not improbable, these -pre-Glacial plants were swept away by the subsequent -arctic conditions, the great majority of them returned -to their old home when a warmer climate ensued. -<span class="pagenum"><a name="Page_48" id="Page_48"> 48 </a></span> -There are however some pre-Glacial plants, such as -the spruce fir (<i>Picea excelsa</i>), a cone of which is -shown in <a href="#Fig_3">Fig. 3, B</a>, the water chestnut, <i>Trapa natans</i> -(<a href="#Fig_4">Fig. 4</a>), and a few other species no longer represented -in the British flora. The genus <i>Trapa</i> is -a striking example of a flowering plant which has -disappeared since the Tertiary period from many -parts of Europe, including England, most of Sweden, -and from several regions in northern Europe. It still -grows in a few localities in Switzerland and in some -of the Italian lakes. In pre-Glacial times the water -chestnut was widely spread from Portugal and England -in the west to Siberia in the east, and its hard four-pronged -nuts have been recorded from many post-Glacial -peat-moors in the north of Europe.</p> - -<div class="fig_center" style="width: 309px;"> -<a name="Fig_4"></a> -<img src="images/fig_4.png" width="309" height="265" alt="" /> -<div class="fig_caption">Fig. 4. <i>Trapa natans</i> Linn. (nat. size). From Mundesley. -(Photographs by Mr and Mrs Reid.)</div> -</div> - -<p>From the so-called Cromer forest-bed and associated -deposits on the Norfolk coast several -pre-Glacial plants have been obtained, indicating -a temperate climate during this phase of the -Pleistocene period. A few arctic species, such as -the dwarf birch and arctic willow obtained from the -deposits next above the Cromer forest-bed, herald -the near approach of glacial conditions.</p> - -<p>It may be remarked in passing that no satisfactory -evidence has been discovered in Britain of the -existence of man in this part of Europe in pre-Glacial -days: it is, however, believed that flints from -Tertiary strata on the continent show traces of human -<span class="pagenum"><a name="Page_49" id="Page_49"> 49 </a></span> -workmanship. As Sir Edwin Ray Lankester said in -1905, 'It is not improbable that it was in the remote -period known as the Lower Miocene—remote as compared -with the gravels in which Eoliths [primitive -stone implements] occur—that Natural Selection -began to favour that increase in the size of the brain -of a large and not very powerful semi-erect ape'(<a href="#Note_28">28</a>).</p> - -<p>Though comparatively recent in terms of geological -chronology, the remoteness, according to ordinary -conceptions of time, of the Tertiary period is brought -home to us when we endeavour to grasp the fact -that it was during this chapter in the earth's history -that some of our highest mountain-ranges, such as -the Alps, the Carpathians, and Himalayas were formed -by the uplifting of piles of marine sediments. From -Tertiary strata in the Isle of Wight, on the Hampshire -coast, and in the London basin numerous fossil -plants have been obtained, which afford convincing -evidence of climatic conditions much more genial -than those of the present day. The presence of palm -leaves and of a wealth of other sub-tropical plants -in Lower Tertiary beds in England reveals the -existence of a flora differing considerably both from -that in the uppermost Tertiary beds of Norfolk and -from the modern British flora, but closely allied to -the present Mediterranean flora.</p> - -<p>The basaltic columns of the Giants' Causeway and -of the Staffa Cave, and the terraced rocks which form -<span class="pagenum"><a name="Page_50" id="Page_50"> 50 </a></span> -so characteristic a feature in the contours of the -Inner Hebrides, are portions of lava-flows, which in -the early days of the Tertiary period were poured -out over a wide area of land stretching from the -north-east of Ireland, through the Western isles of -Scotland, the Faro islands, to Iceland and Greenland. -While in this northern region volcanic activity was -being manifested on a stupendous scale, a shallow -sea extended over part of what is now the south-east -of England in which was deposited a considerable -thickness of sedimentary material derived from the -neighbouring land. In this upraised sea-floor, known -as the London clay, which is exposed in the Isle of -Sheppey and in many other localities, numerous fossil -fruits and fragments of wood occur in association -with marine shells. The fact that many of the fruits -were ripe at the time of their entombment led some -eighteenth century writers to assign an autumn date -to the universal deluge. One of the Sheppey fruits -may be mentioned as an especially interesting sample -of the early Tertiary flora, namely the genus Nipadites, -so named from the very close resemblance of -the fossils to the fruits of the existing tropical plant -Nipa. <i>Nipa fruticans</i>, sometimes described as a -stemless palm because of the absence of the erect -stem which is usually a characteristic feature of -palms, grows in brackish estuaries of many tropical -countries (<a href="#Fig_5">Fig. 5, A</a>): it has long leaves not unlike -those of the date-palm and bears clusters of fruits -as large as a man's head; a single fruit is two or -three inches long and its hard fibrous shell is characterised -by four or five longitudinal ribs (<a href="#Fig_5">Fig. 5, B</a>). -The fruits of Nipa, which may be carried a considerable -distance by ocean-currents without losing the -power of germination, are constantly found with other -vegetable drift on the beaches of tropical islands. The -discovery of fruits of Nipa (or Nipadites), hardly -distinguishable from those of the existing species, -in Tertiary beds in England, Belgium, in the Paris -basin, and in Egypt affords a striking instance of -changes in the geographical distribution of an ancient -plant now restricted to warmer regions.</p> - -<p><span class="pagenum"><a name="Page_51" id="Page_51"> 51 </a></span></p> - -<div class="fig_center" style="width: 512px;"> -<a name="Fig_5"></a> -<img src="images/fig_5.png" width="512" height="350" alt="" /> -<div class="fig_caption">Fig. 5. <i>Nipa fruticans</i>, Thunb. A. On the coast of the Malay Peninsula. (Photograph -by Prof. Yapp.) B. Head of fruits (<sup>1</sup>/<sub>5</sub> nat. size). From a specimen in the British Museum.</div> -</div> - -<p><span class="pagenum"><a name="Page_52" id="Page_52"> 52 </a></span></p> - -<p>While the higher members of the Cretaceous -system, as seen in the chalk cliffs and downs, represent -the upraised calcareous accumulations on -the floor of a fairly deep and clear sea, the lower -members testify to shallower water within reach of -river-borne sand and mud. 'During the Chalk -period,' as Huxley wrote, 'not one of the present -great physical features of the globe was in existence. -Our great mountain ranges, Pyrenees, Alps, Himalayas, -Andes, have all been upheaved since the -chalk was deposited, and the Cretaceous sea flowed -over the sites of Sinai and Ararat'(<a href="#Note_29">29</a>).</p> - -<p>The Wealden strata, at the base of the Cretaceous -system, as seen on the Sussex coast, in parts of the -<span class="pagenum"><a name="Page_53" id="Page_53"> 53 </a></span> -Isle of Wight, in the Weald district of Kent and -neighbouring counties, point to the existence of a -lake over a portion of the south of England and of -the English Channel. The remains of a rich Wealden -flora have been collected from these Wealden sediments, -notably from the plant-beds of Ecclesbourne -near Hastings, in which, so far as we know, flowering -plants played no part or at most occupied a very -subordinate position. A few fossil leaves have been -described from rocks assigned to a Wealden age,—and -from the older Stonesfield Slate, of Jurassic -age, a single leaf is recorded,—which seem to be -those of Dicotyledons; but it is certain that even in -the early days of the Cretaceous period the present -dominant group in the plant kingdom was in its -infancy and in many regions probably unrepresented. -When we glance at the geological table and consider -that in all the floras from the Wealden down to the -Devonian period, flowering plants played no part, -we are able to appreciate the fact of their rapid -development, referred to in a previous chapter, when -once this highest type had become established.</p> - -<p>The rocks comprised in the Jurassic system extend -from East Yorkshire to the coast of Dorsetshire; they -consist of a succession of limestones, clays, sandstones, -and a few thin beds of impure coal. Sediments of -this age also occur, though to a much less extent, -on the north-east coast of Scotland and in a few -<span class="pagenum"><a name="Page_54" id="Page_54"> 54 </a></span> -places in the Inner Hebrides. Many of the Jurassic -strata contain only marine shells, and corals are -occasionally abundant, though in the lower members -of the system in the cliffs near Lyme Regis and at -Whitby fossil plants are fairly common. It is, however, -from the middle Jurassic beds, in the cliffs -between Whitby and Scarborough, and in some -inland quarries in East Yorkshire, that we have -obtained the richest Jurassic flora. Rivers from a -northern land laden with sediment and carrying drift-wood, -leaves and other plant fragments, deposited -their burden in an estuary which occupied the eastern -edge of Yorkshire. Sedimentary rocks laid down -towards the close of the Jurassic period in the island -of Portland in the south and on the Sutherland coast -in the north have furnished valuable records of -plant-life.</p> - -<p>The passage from the Jurassic to the underlying -Triassic system is formed by some shales and limestones -in South Wales containing remains of fish and -other marine organisms. These so-called Rhaetic -beds are poorly represented in the British area, but -on the continent of Europe and in other regions the -sediments of this age bulk much more largely and -have yielded a rich collection of plants. The rocks -of the upper division of the Triassic system, as seen -in the Midlands, point to the prevalence of desert -conditions; and in the grooved sand-polished surfaces -<span class="pagenum"><a name="Page_55" id="Page_55"> 55 </a></span> -of granite in Charnwood forest we have a glimpse of -a Triassic landscape. The salt-bearing strata of this -period in Cheshire and Worcestershire suggest conditions -paralleled at the present day in the Caspian -and Dead-Sea regions. The vegetation of Britain, and -indeed of the world as a whole, seems to have undergone -but little change during the enormous lapse of -time represented by the sediments comprised between -the Wealden and Triassic periods. The Lower Triassic -flora affords evidence of a change in the facies of the -vegetation and prepares us for the still greater differences -revealed by a study of the Permian and -Carboniferous floras. To the student of evolution -these Palaeozoic floras are of special interest on -account of the facts they have contributed in regard -to the descent and inter-relationship of different -branches of the vegetable kingdom.</p> - -<p>It is by a patient study of the waifs and strays -of the vegetation of successive phases of the world's -history preserved in sedimentary strata, that it has -been possible to follow the history of many existing -plants and to establish links between the present -and the past.</p> -<hr class="chap" /> - -<p><span class="pagenum"><a name="Page_56" id="Page_56"> 56 </a></span></p> - - - -<h2><a name="CHAPTER_IV" id="CHAPTER_IV">CHAPTER IV</a></h2> - -<p class="caption3">PRESERVATION OF PLANTS AS FOSSILS</p> - -<p class="smaller">'Some whim of Nature locked them fast in stone for us afterthoughts -of Creation.' <span class="smcap">Lowell.</span></p> - - -<p>The failure of the earlier naturalists to grasp the -true significance of fossils or even to appreciate their -nature is an extraordinary fact when we consider the -pioneer work which they accomplished in biological -and geological science. The following extract from -the writings of so enlightened a man as John Ray -serves to illustrate an almost incredible disinclination -to admit what seems to us the obvious. He wrote:—'Yet -I must not dissemble that there is a Phenomenon -in Nature, which doth somewhat puzzle us to -reconcile with the prudence observable in all its -work, and seems strongly to prove, that Nature doth -sometimes <i>ludere</i>, and delineates figures, for no other -end, but for the ornament of some stone, and to -entertain or gratify our curiosity, and exercise our -wits. This is, those elegant impressions of leaves and -<span class="pagenum"><a name="Page_57" id="Page_57"> 57 </a></span> -plants upon cole-slate, the knowledge of which, -I must confess myself to leave to my learned and -ingenious friend Mr Edward Lhwyd of Oxford.... He -told me that Mr Woodward, a Londoner, shewed -him very good draughts of the common female fern, -naturally formed in cole.... But these figures are more -diligently to be observed and considered... Dr Woodward -will have them to be the impressions of the -leaves of plants which were there lodged at the time -of the Deluge'(<a href="#Note_31">31</a>).</p> - -<p>The Mr Woodward alluded to by Ray thus -expressed his views on fossils in an <i>Essay towards -the Natural History of the Earth</i>:—'The whole -terrestrial globe was taken all to pieces and dissolved -at the Deluge, the particles of stone, marble, and -all solid fossils dissevered, taken up into the water, -and then sustained together with sea shells and other -animal and vegetable bodies; the present earth -consists and was formed out of that promiscuous mass -of sand, earth, shells, and the rest falling down again, -and subsiding from the water'(<a href="#Note_32">32</a>).</p> - -<p>In the later part of the seventeenth-century -Steno, a Dane by birth and Professor of Anatomy at -Padua, by his recognition of the identity of the teeth -in a shark's head, which he had dissected, with some -fossils from Malta known as Glossopetrae, established -the true nature of fossils. He also recognised a -certain orderly sequence in fossiliferous strata, and -<span class="pagenum"><a name="Page_58" id="Page_58"> 58 </a></span> -in the opinion of Professor Sollas he is entitled to -be considered the 'Father and Founder' of Geology(<a href="#Note_33">33</a>).</p> - -<p>It was by slow degrees that the early observers -freed themselves from the obsession that the remains -of animals and plants in the earth's crust bear witness -to a Universal Deluge and are all identical with -existing species. The possibility that some of the -fossil plants in English strata might be more clearly -related to forms now met with in warmer regions -was gradually realised. The publication of the -<i>Origin of Species</i> stimulated palaeontological -research, and botanists as well as zoologists turned -to the investigation of extinct genera in search of -proofs of the doctrine of evolution.</p> - -<p>The common occurrence of petrified wood in -rocks of different ages is well known. Fossil stems -are occasionally found in their natural position of -growth, the structural details being rendered permanent -by the deposition of siliceous or calcareous -material from water drawn by capillarity into the -dead but still sound tissues. Petrified wood from -Upper Jurassic beds is abundant in the Island of -Purbeck; an unusually long piece of stem may be -seen in the small town of Portland fixed to the wall -of a house. Some of these stems have been referred -by an American author to the Araucarian family of -Conifers, but the structure is as a rule hardly well -enough preserved to afford satisfactory evidence for -<span class="pagenum"><a name="Page_59" id="Page_59"> 59 </a></span> -identification. In his <i>Testimony of the Rocks</i>, Hugh -Miller speaks of fossil wood from the upper beds of -the Jurassic system in sufficient abundance on the -beach at Helmsdale in Sutherlandshire to be collected -in cart-loads; it is still easy to pick up good specimens -on the shingle beach a short distance north of -Helmsdale, and a recent microscopical examination -showed that some specimens are pieces of an Araucarian -tree.</p> - -<p>Impressive examples of petrified trees on a -large scale are to be seen in the United States, -in Arizona and the Yellowstone Park. (Frontispiece.) -In the northern part of Arizona the country for over -an area of 10 square miles is covered with tree trunks, -some reaching 200 feet in length and a diameter of -10 feet. The nature of the mineralising substance has -given rise to the name Chalcedony Park for this -Triassic forest(<a href="#Note_34">34</a>). A striking example of one of the -Arizona trees is exhibited in the British Museum and -in a neighbouring case is a splendid petrified stem, 9 ft. -in height, of a conifer discovered in Tertiary lavas in -Tasmania(<a href="#Note_35">35</a>).</p> - -<p><span class="pagenum"><a name="Page_60" id="Page_60"> 60 </a></span></p> - -<div class="fig_center" style="width: 365px;"> -<a name="Fig_6"></a> -<img src="images/fig_6.png" width="365" height="488" alt="" /> -<div class="fig_caption">Fig. 6. Section of the north face of Amethyst Mountain, Yellowstone -Park, including upwards of 2000 ft. of strata. The -steepness of the slope is exaggerated. (After W. H. Holmes.)</div> -</div> - -<p><span class="pagenum"><a name="Page_61" id="Page_61"> 61 </a></span></p> - -<p><a href="#Fig_6">Figure 6</a> illustrates the preservation of a series -of forests of Tertiary age in the mass of volcanic -sediments, 2000 feet in thickness, known as Amethyst -mountain, in the Yellowstone Park district. By the -weathering away of the surrounding volcanic material -the tall stems of the trees are exposed in places on -the mountain sides like the 'columns of a ruined -temple.' The height of the river at the foot of the -cliff is 6700 ft. above sea-level and the mountain -rises to a height of 9400 ft. above the sea. In the -lower part of the section the volcanic strata are seen -to rest on a foundation of older rocks <i>A</i>, and these -in turn were laid down on the eroded surface of a -still more ancient foundation, <i>B</i>(<a href="#Note_36">36</a>).</p> - -<p>The section as a whole affords a striking demonstration -of the magnitude of earth-movements since -the last of these forests was buried below the -surface of a sea in which the volcanic material was -deposited. The account of the Yellowstone Park -section recalls Darwin's description in the <i>Naturalist's -Voyage</i>(<a href="#Note_37">37</a>) of snow-white columns projecting -from a bare slope, at an altitude of 7000 ft. in the -Cordillera.</p> - -<p>The abundance of drift-wood on the coasts of -some countries at the present day helps us to picture -the conditions under which the remains of former -forests have been preserved. In his <i>Letters from -High Latitudes</i>, Lord Dufferin gives the following -description of drift-wood on the shores of Spitzbergen:—'A -little to the northward, I observed, -lying on the sea-shore innumerable logs of drift-wood. -This wood is floated all the way from America by the -Gulf Stream, and as I walked from one huge bole -to another, I could not help wondering in what -<span class="pagenum"><a name="Page_62" id="Page_62"> 62 </a></span> -primeval forest each had grown, what chance had -originally cast them on the waters, and piloted -them to this desert shore'(<a href="#Note_38">38</a>). A photograph reproduced -in Amundsen's book on <i>The North West -Passage</i> shows the beach on the Alaskan coast -strewn with drifted timber(<a href="#Note_39">39</a>). For the accompanying -photograph (<a href="#Fig_7">Fig. 7</a>) of the flood-plain of the Colorado -River(<a href="#Note_40">40</a>), I am indebted to Professor MacDougal of -the Desert Research Laboratory at Tucson, Arizona, -who in a recent letter writes, 'During times of high-water -a thin sheet of flood covers the flat for many -miles and bears drift-wood so thickly that it is -difficult to push a boat through it.' The drift-wood -consists of poplar, willow, pine, and juniper, 'the last -two have been brought from the upper river, from -as far away as a thousand miles.' A picture such as -this affords an admirable example of the wealth -of material available for preservation in a fossil state.</p> - -<p>It is only in the minority of cases that the -accidents of preservation of fragments of ancient -floras have given us the means of investigating the -internal structure of the plant organs. It is far more -frequently the case that fossil plants are represented -only by a carbonised film on the surface of a piece of -shale or other rock: the actual substance of the -plant has been converted into a thin layer of coal, -and though the venation and other surface-features -may be clearly revealed, the internal tissues have -been destroyed. If a lump of clay containing a -piece of fern frond is heated, the result is an impression -of the leaf on the hardened matrix and a -coaly substance in place of the plant substance. It -is occasionally possible by detaching a piece of the -black film from a fossil, and heating it with nitric -acid and chlorate of potash and then dipping it in -ammonia, to obtain a transparent preparation suitable -for microscopical examination of the cell-outlines -of the superficial layer of the leaf or other plant-fragment. -This method of examination, used by -several students of fossil plants and with conspicuous -success by Professor Nathorst of Stockholm, often -affords valuable aids to identification.</p> - -<p><span class="pagenum"><a name="Page_63" id="Page_63"> 63 </a></span></p> - -<div class="fig_center" style="width: 368px;"> -<a name="Fig_7"></a> -<img src="images/fig_7.png" width="368" height="478" alt="" /> -<div class="fig_caption">Fig. 7. Flood-plain of the delta of Rio Colorado. The hills in -the background are 25 miles distant. (From a photograph by -Prof. MacDougal.)</div> -</div> - -<p><span class="pagenum"><a name="Page_64" id="Page_64"> 64 </a></span></p> - -<p>Pieces of plants embedded in sandy sediment, -if not preserved by petrifaction, that is by the -introduction into the tissues of some siliceous -or calcareous solution, gradually decay and their -fragmentary remains may be washed away by -percolating water, leaving a hollow mould in the -gradually hardening sediment, which is afterwards -filled with sand or other material. The plant itself -is destroyed, but a cast is taken which in the case -of fine-grained sediments reproduces the form and -surface-pattern of the original specimen. The incrustation -of plants by the falsely named petrifying -springs of Knaresborough and other places illustrate -another method of fossilisation.</p> - -<p><span class="pagenum"><a name="Page_65" id="Page_65"> 65 </a></span></p> - -<div class="fig_center" style="width: 350px;"> -<img src="images/fig_8.png" width="350" height="249" alt="" /> -<div class="fig_caption"><a name="Fig_8"></a>Fig. 8. Flower of <i>Cinnamomum prototypum</i> Conw. preserved in -amber. × 10. (After Conwentz.)</div> -</div> - -<p>Plants which owe their preservation to amber -occur both as incrustations and petrifactions. This -fossil resin occurs in Tertiary, Cretaceous, and -Jurassic rocks; the amber found in abundance on -the Baltic coast near Danzig and occasionally picked -up on the beach in Norfolk and Suffolk comes from -beds of Tertiary age. Pieces of Pine-wood have been -described from the Baltic beds in which the tissues -are perfectly preserved as the result of the conversion -into amber of the resinous secretion which permeates -their cells: in this case the amber is a petrifying -<span class="pagenum"><a name="Page_66" id="Page_66"> 66 </a></span> -agent. More frequently the preservation is due to -incrustation; as resin trickled down the stems of the -Tertiary pines from an open wound, flowers and -leaves, blown by the wind on to the sticky surface, -were eventually sealed up in a translucent case of -amber. Though the actual substance may have gone, -the mould which remains exhibits in wonderful perfection -each separate organ of a flower or the -delicate hair-clusters on the surface of a leaf. The -flower represented in <a href="#Fig_8">Fig. 8</a>, a species of Cinnamon, -is one of several specimens described by the authors -of a monograph of Tertiary plants in the Baltic -amber(<a href="#Note_41">41</a>).</p> - -<p>The fragments of plants preserved in nodules of -calcareous rock occasionally met with in some of the -Lancashire and Yorkshire coal-seams are perhaps -the most striking examples of the possibilities of -petrifaction. By cutting sections of these nodules -and grinding them to a transparent thinness, the -most delicate tissues of Carboniferous plants are -rendered accessible to investigation under the high -power of a microscope. As our attention is absorbed -by the examination of the details of cell-structure -it is easy to forget that the section has not been -cut from a living plant, but from the twig of a -tree which grew in the forests of the Coal age. The -preservation is such as to enable us not only to -describe the anatomy of these extinct types of -<span class="pagenum"><a name="Page_67" id="Page_67"> 67 </a></span> -vegetation, but, by the application of the knowledge -of the relation between the structure of the plant-machine -and its functions gained by a study of living -species, it is possible in some degree to picture the -plants of the Coal period as living organisms and -to see in the structural framework a reflection of -external environment. The recognition in the general -architectural plan of the Palaeozoic plants, as in -many of the finer anatomical features, of the closest -resemblance to plants of the modern world produces -an almost overwhelming sense of continuity between -the past and the present.</p> - -<p>The plants of the Palaeozoic period, though often -differing considerably from those of the same class -in the floras of to-day, exhibit a remarkably high type -of organisation. Some of the most abundant trees in -the forest of the Coal age are decidedly superior -in the complexity of their structure, as also in -size, to modern survivals of the same stock. On -the other hand, it must be remembered that Monocotyledons -and Dicotyledons which now occupy the -highest place in the hierarchy of plants have left no -sign of their existence in any of the Palaeozoic strata. -The greater size of some of the Palaeozoic plants, -and in some respects the more advanced stage of -evolution which they represent as compared with -their nearest relatives of the present era, must be -considered in relation to their more important and -<span class="pagenum"><a name="Page_68" id="Page_68"> 68 </a></span> -relatively higher position in the plant-world than -that which is now held by their diminutive descendants. -It is, however, impossible to get away -from the conclusion that the oldest Palaeozoic flora -of which we have an intimate knowledge must be -the product of development of an age which is -represented by a chapter in the history of the plant -kingdom at least as far removed from the beginning -as it is separated from the chapter now being written. -Examples might be quoted in illustration of the risks -attending the determination of fossils by means of -external features alone, but it may suffice to mention -the case of a specimen originally described as a -fragment of a Cretaceous Dinosaur under the name -<i>Aachenosaurus multidens</i>. By the examination of -thin sections this supposed bone was shown to be -a piece of Dicotyledonous wood(<a href="#Note_42">42</a>). The methods of -preservation of plants as fossils are numerous and -varied and the few examples selected give but an -incomplete idea of the subject: for a fuller treatment -of fossilisation the reader is referred to more technical -treatises (48 vol. <span class="smcap">I</span>.).</p> - -<p>The employment of fossil plants as 'Thermometers -of the ages' is a branch of Palaeobotany to which a -passing allusion may be permitted though it is only -indirectly connected with the main question. As -one of the most interesting examples of changed -climatic conditions revealed by a study of fossil plants, -<span class="pagenum"><a name="Page_69" id="Page_69"> 69 </a></span> -reference may be made to the wealth of material -collected within the Arctic circle. The problems -suggested by the discovery of plants in rocks of -various ages in North Siberia, Spitzbergen, Franz -Josef Land, Bear Island, Greenland, and in many -other localities in the far north are too difficult -and far-reaching to be discussed in these pages. In -the Cretaceous and Tertiary strata of the west coast -of Greenland and Disco Island from 69° to 72° north -latitude, to refer only to one case, a great number -of plants have been obtained by several of the earlier -Arctic explorers and more recently by members of -one of the Peary Expeditions. At the present day -on the fringe of land on the western edge of Greenland -which is not permanently covered with ice, -a considerable number of herbaceous plants are able -to exist and to produce seed during their concentrated -period of development; while trees are represented -only by a few low-growing shrubs such as the dwarf -Juniper. In places accessible to investigation beyond -the ice-covered hills of northern Greenland the rocks -have been shown to consist of Cretaceous and Tertiary -sediments containing fossil plants associated with -seams of coal. From these beds numerous Dicotyledons -have been obtained, some of them almost -identical with living species characteristic of sub-tropical -or tropical countries. In the lowest of the -Cretaceous series no Dicotyledons have been found, -<span class="pagenum"><a name="Page_70" id="Page_70"> 70 </a></span> -but flowering plants are abundant in the higher -Cretaceous rocks. Allowing for the fact that closely -allied species are often able to live under very -different climatic conditions, there can be no doubt -that the Cretaceous and Tertiary floras of Greenland -indicate an average temperature considerably higher -than that which now prevails in the warmest parts -of the British Isles.</p> - -<p>In the far south a fairly rich Jurassic flora has -recently been discovered by the members of a -Swedish Antarctic expedition in Graham's Land in -latitude 63°15 S. and longitude 57° W., which in its -general facies bears a close resemblance to the -Jurassic flora of Yorkshire.</p> - -<p>Although the great majority of the records of -ancient plants are difficult to interpret by reason -of imperfect preservation and because of the frequent -separation of leaves, stems, and reproductive organs, -the student who tries to piece together the <i>disjecta -membra</i> of the floras of the past shares the opinion -expressed by the late Marquis of Saporta,—'Si l'on -s'attache les dchiffrer, on oublie bien vite la -singularit des caractres, et le mauvais tat des -pages. La pense se lve, les ides se dveloppent, -le manuscrit se droule; c'est la tombe qui parle et -livre son secret.'</p> -<hr class="chap" /> - -<p><span class="pagenum"><a name="Page_71" id="Page_71"> 71 </a></span></p> - - - -<h2><a name="CHAPTER_V" id="CHAPTER_V">CHAPTER V</a></h2> - -<p class="caption3">FERNS; THEIR DISTRIBUTION AND ANTIQUITY</p> - -<p class="smaller">'It has been shown that certain forms persist with very little -change, from the oldest to the newest fossiliferous formations; and -thus show that progressive development is a contingent, and not -a necessary, result of the nature of living matter.' <span class="smcap">Huxley.</span></p> - - -<p>The Ferns as a whole represent a section of the -vegetable kingdom which traces its ancestry as far -into the past as any group of plants. Impressions of -leaves on the shales of the Coal-measures and on -rocks of the earlier Devonian period are hardly -distinguishable in form and in the venation and -shape of the leaflets from the finely divided fronds -of modern ferns. Until a few years ago these -Palaeozoic fossils were generally regarded as true -ferns, and it was believed that ferns played a conspicuous -part in the vegetation of the earliest periods, -of which we have any botanical knowledge. Conclusions -based on external form must frequently be -<span class="pagenum"><a name="Page_72" id="Page_72"> 72 </a></span> -revised in the light of more trustworthy evidence. -It was shown in the later part of the nineteenth -century by the late Professor Williamson of Manchester, -whose researches into the plants of the -Coal age shed a flood of light on the ancestry and -inter-relationship of many existing plants, that some -of the fern-like leaves which have long been familiar -to those who search among the shales of the refuse -heaps of collieries, were borne on stems differing in -anatomical features from those of any known fern. -The investigation of the structure of the leaves and -their supporting stems led to the recognition of -certain extinct genera of Palaeozoic plants of exceptional -interest, to which the term generalised type is -aptly applied. Associated with anatomical and other -characters such as we now regard as the attributes -of ferns, these plants exhibit other features not met -with in modern ferns but characteristic of a group of -seed-bearing plants known as the Cycads. Recent -research has revealed the existence of several such -generalised types which, by their combination of -characters now met with in distinct sub-divisions -of the plant-kingdom, clearly indicate the derivation -of Ferns, and Cycads as we know them to-day, from -a common stock. It was in the first instance by -means of anatomical evidence—obtained by the -microscopical examination of sections of petrified -fragments of stems and leaves—that the generalised -<span class="pagenum"><a name="Page_73" id="Page_73"> 73 </a></span> -nature of these Palaeozoic plants was recognised. -Nothing was known as to the reproductive organs. -Ferns as now represented in the floras of the -world are essentially seed-less plants. As the author -of <i>Hudibras</i> wrote:</p> - -<div class="poem"><div class="stanza"> -<span class="i0">'Who would believe what strange bugbears<br /></span> -<span class="i1">Mankind creates itself, of fears?<br /></span> -<span class="i1">That spring like fern, that insect weed,<br /></span> -<span class="i1">Equivocally, without seed.'<br /></span> -</div></div> - -<p>The reproductive organs or spores borne on the -fronds of a fern produce, on germination, a thin -green structure, known as the prothallus, less than -an inch in length: this bears the sexual organs, and as -the result of the union of the male and female cells, -the embryo fern-plant begins its existence as a parasite -on the inconspicuous prothallus, until after unfolding -its first green leaf and thrusting a slender root into -the ground, it starts its career as an independent -organism<a name="FNanchor_2" id="FNanchor_2"></a><a href="#Footnote_2" class="fnanchor">[2]</a>. In this life-cycle the seed plays no -part.</p> - -<div class="footnote"> - -<p><a name="Footnote_2" id="Footnote_2"></a><a href="#FNanchor_2"><span class="label">[2]</span></a> The life-history of a Fern is clearly described by Prof. Bower -in a recent volume in this series.</p></div> - -<p>It is noteworthy that the absence of any indication -of spore-capsules and spores, in the case of some of -the supposed fern leaves from the Coal-measures, -caused some suspicion in the mind of an Austrian -Palaeobotanist as to the right of such specimens to -<span class="pagenum"><a name="Page_74" id="Page_74"> 74 </a></span> -be classed among the ferns. This opinion, based in -the first place on negative evidence and but little -regarded by other authors, has in recent years -been proved correct. In 1904 a paper was read -before the Royal Society by Professor Oliver and -Dr Scott(<a href="#Note_43">43</a>) in which evidence was brought forward -pointing to the conclusion that one of these -generalised plants bore true seeds. Subsequently -Dr Kidston published an account of some specimens -of another of these Palaeozoic plants in which was -actually shown an organic connexion between undoubted -seeds and pieces of a fern-like frond(<a href="#Note_44">44</a>). -Without entering into further details, these and -similar discoveries may be summarised as follows:—Many -of the supposed Fern-fronds of Palaeozoic -age, particularly those characteristic of the Coal-measures, -are the leaves of plants which in their -anatomical characters combined features now shared -by true Ferns and by the Cycads. The reproductive -organs of these Palaeozoic genera differed widely -from those of existing ferns; the male organs, while -not unlike the spore-capsules and spores of certain -ferns, recall the male organs of living Conifers and -Cycads, and the female organs were represented by -seeds of a highly complex form. These seed-bearing -plants have been called Pteridosperms, a name -which expresses the combination of fern-like features -with one of the distinguishing attributes of the -<span class="pagenum"><a name="Page_75" id="Page_75"> 75 </a></span> -higher plants, namely the possession of seeds. The -ancestors of Pteridosperms are as yet unknown; it -is, however, reasonable to assume that there existed -in some pre-Carboniferous epoch a group of simple -plants from which both Ferns and Pteridosperms -were derived. In the forests of the Coal age true -Ferns probably occupied a subordinate position in -relation to the Pteridosperms.</p> - -<p>The question of the relationship between different -families of recent ferns and the older known fossil -members of the group is beyond the scope of this -book. Evidence has been discovered in recent years -which warrants the statement that, although none of -those Carboniferous ferns were generically identical -with existing forms, they very clearly foreshadowed -some of those structural features which characterise -more than one family of present-day Ferns. The -records of the older Mesozoic formations afford -abundant evidence of the existence of certain types -of Ferns showing a very close resemblance to recent -species.</p> - -<p><span class="pagenum"><a name="Page_76" id="Page_76"> 76 </a></span></p> - -<div class="fig_center" style="width: 370px;"> -<img src="images/fig_9.png" width="370" height="467" alt="" /> -<div class="fig_caption"><a name="Fig_9"></a>Fig. 9. <i>Osmunda regalis</i> Linn. Fertile frond, (<sup>2</sup>/<sub>5</sub> nat. size.)</div> -</div> - -<p><span class="pagenum"><a name="Page_77" id="Page_77"> 77 </a></span></p> - -<p>An enquiry into the geographical distribution of -living Ferns reveals facts of special interest in -connexion with the relative antiquity of different -genera and families. The wide distribution of the -Bracken fern has already been referred to: it is -abundant in Tasmania; its vigour in the island -is well illustrated by Mr Geoffrey Smith's statement -that constant attention is necessary to keep it from -invading newly opened country(<a href="#Note_45">45</a>). On Mount Ophir -in the Malay Peninsula the cosmopolitan bracken -occurs in association with the two genera Matonia -and Dipteris, ferns which are among the most striking -examples of links with a remote past and have a -restricted geographical range. With <i>Osmunda regalis</i>, -the Royal Fern, the Bracken is conspicuous -in the marsh vegetation of the Bermudas; it flourishes -on the Atlas Mountains, in the Canary Islands, in -Abyssinia, on Mt Kenia, in British East Africa, in -the Himalayas, and is in fact generally distributed in -the tropics in both the north and south temperate -zones.</p> - -<p>The Royal Fern (<a href="#Fig_9">Fig. 9</a>) is another British species -with a wide distribution; it occurs in Northern Asia -and in North America; it is common in the Siberian -forests and lives in several tropical countries, extending -to Southern India and Cape Colony, and in -South America it is represented by a closely allied -species. Though at the present day <i>Osmunda regalis</i> -is one of the rare English Ferns, its occurrence in the -submerged forest-beds round our coasts and in pre-Glacial -beds points to its former abundance in the -British area generally. The Royal Fern is a member -of a family now represented by two genera, Osmunda -and Todea.</p> - -<p>With the exception of <i>Todea barbara</i>, with its -<span class="pagenum"><a name="Page_78" id="Page_78"> 78 </a></span> -large spreading fronds and a short root-covered stem, -which occurs in Australia and Cape Colony, all the -species of this genus are filmy ferns with semitransparent -fronds adapted to a moisture-laden -atmosphere. The maximum development of the genus is in New Zealand.</p> - -<p><i>Todea barbara</i> affords an instance of discontinuous -distribution; it was no doubt once widely spread in -circumpolar regions and now survives only in South -Africa and in Australia.</p> - -<p>There are satisfactory reasons for regarding the -Bracken Fern, with its world-wide range in present-day -floras, as a comparatively modern species now in -full vigour. Its anatomical and other features are -consistent with the view that it is a late product of -evolution, and as yet no indication has been given by -the records of the rocks of an ancient lineage. The -Osmunda family, on the other hand, is undoubtedly -an extremely old branch of the fern group. A comparison -of the Royal Fern with the Bracken shows -that their stems are constructed on very different -plans, and we have good reasons for speaking of the -structural peculiarities of the former as those of -a more primitive type. Moreover, the discontinuous -geographical range of some members of the Osmunda -family is in itself an indication of antiquity. There -<span class="pagenum"><a name="Page_79" id="Page_79"> 79 </a></span> -is another point which may have a bearing in this -question of antiquity, namely the fact that the spores -of Osmunda are green and do not possess the powers -of indurance inherent in the spores of the majority of -ferns which are not green. It has recently been contended -by Professor Campbell of Stanford University -that the delicate green spores of the Liverworts, -plants closely allied to the Mosses, constitute an -argument in favour of the antiquity of these plants(<a href="#Note_46">46</a>). -Certain Liverworts are cosmopolitan in their range, -<i>e.g.</i> the genera Riccia and Marchantia.</p> - -<p>If certain genera are widely distributed, notwithstanding -the fact that their reproductive cells, by -which dispersal is effected, are ill-adapted to withstand -unfavourable conditions or to endure prolonged -desiccation, it would seem reasonable to conclude -that their emigration has been accomplished slowly -and with difficulty. Ferns such as Osmunda, with -green and short-lived spores, would thus be handicapped -in competition with other genera provided -with more efficient means of dispersal and better -equipped for the vicissitudes of travel.</p> - -<p>The inferences as to antiquity deduced from a -study of the existing species of Osmunda and Todea -receive striking confirmation from the testimony of -fossils. Some of the oldest known Palaeozoic ferns, -though differing too widely from the existing Osmundas -and Todeas to be included in the same family, afford -<span class="pagenum"><a name="Page_80" id="Page_80"> 80 </a></span> -distinct glimmerings of Osmundaceous characters, -which at a later period became individualised in -the direct ancestors of the modern forms. Our -knowledge of the past history of the Osmunda family -has recently been considerably extended and placed -on a firmer basis by the researches of Dr Kidston -and Professor Gwynne-Vaughan. These authors have -recognised in some exceptionally well-preserved fern-stems -from Permian rocks in Russia, anatomical -features which point unmistakably to close relationship -with the recent members of the family(<a href="#Note_47">47</a>)(<a href="#Note_48">48</a>).</p> - -<p>Passing higher up the geological series, fertile -fern fronds with spore-capsules and spores practically -identical with those of Osmunda have been found in -the Jurassic plant-beds of Yorkshire and in rocks -of approximately the same age in many parts of the -world. From Jurassic strata in New Zealand a -petrified fern-stem has been described (<i>Osmundites -Dunlopi</i>), almost identical in structure with the -surviving species. Cretaceous and Tertiary examples -of similar ferns might be quoted; but enough has -been said to establish the claim of the Royal Fern -and other members of the Osmunda-family to an -ancestry which possibly extends even farther back -than that of any other existing family of Ferns.</p> - -<p><span class="pagenum"><a name="Page_81" id="Page_81"> 81 </a></span></p> - -<div class="fig_center" style="width: 384px;"> -<img src="images/fig_10.png" width="384" height="321" alt="" /> -<div class="fig_caption"><a name="Fig_10"></a>Fig. 10. <i>Gleichenia dicarpa</i> Br. (<sup>1</sup>/<sub>2</sub> nat. size.)</div> -</div> - -<p>A brief reference may be made to another fern now -represented by several species widely disseminated -in tropical and sub-tropical countries. The genus -Gleichenia occurs abundantly in the warmer regions -of both the Old and New World. The fronds may -usually be recognised by their habit of growth -(<a href="#Fig_10">Fig. 10</a>); in several species the main axis is -repeatedly forked and a small bud between the -divergent branches of the forks forms a characteristic -feature. The leaflets are either long and narrow -<span class="pagenum"><a name="Page_82" id="Page_82"> 82 </a></span> -like the teeth of a comb or short and bluntly rounded. -Moreover the anatomy of the creeping stem affords -a ready means of identification. We have satisfactory -evidence of the occurrence of Gleichenia in European -floras during both the Jurassic and Cretaceous -periods. Numerous fragments of plants were obtained -some years ago, not far from Brussels, from the Wealden -strata in which the famous skeletons of Iguanodon -were discovered. Visitors to the Natural History -Museum in Brussels are no doubt familiar with the -skeletons of this enormous herbivorous animal: in -the same gallery are exhibited the remains of the -fossil plants from the Iguanodon beds. Some of -these fragments are pieces of fern fronds identical -in form with those of existing Gleichenias. The -microscopical examination of some exceptionally well -preserved fragments of Wealden stems discovered by -Prof. Bommer of Brussels enabled him to recognise -the Gleichenia type of structure and thus to confirm -the inconclusive evidence furnished by fragmentary -leaves. The most interesting records in regard to -the former occurrence of Gleichenia in Northern -Europe we owe to the late Oswald Heer of Zurich, -who has described many examples of Gleichenia -fronds from rocks of Lower Cretaceous age in -Disco Island on the west coast of Greenland in -latitude 70° N. The same type of fern is recorded -also from upper Jurassic beds in the north-east of -<span class="pagenum"><a name="Page_83" id="Page_83"> 83 </a></span> -Scotland, in the Wealden rocks of Sussex, as well as -from other European localities. It is clear that the -Gleichenia-family, no longer represented in north -temperate floras, was in the Jurassic period, and -especially in the early days of the Cretaceous period, -widely spread in Europe, extending well within the -Arctic circle. It may be that the original home of -Gleichenia was in the far North at a time when -climatic conditions were very different from those -which now prevail. Gleichenia, like many other -northern plants, retreated to more southern regions -where, in the warmer countries of the world, many -species still flourish widely separated in space and -time from the place of their birth.</p> - -<p>The ferns so far mentioned have a more or less -extended distribution at the present day. In the -case of <i>Pteridium aquilinum</i>, the cosmopolitan -Bracken Fern, wide range would seem to be correlated -with comparatively recent origin; on the -other hand, the facts of palaeobotany show that -the wide distribution of Osmunda, a type of fern -which differs in many important respects from -members of the family (Polypodiaceae) to which -the Bracken belongs, is not inconsistent with an -exceptionally ancient family-history. There are, -however, certain genera of ferns which afford -remarkable examples of restricted geographical -distribution associated with great antiquity. The -<span class="pagenum"><a name="Page_84" id="Page_84"> 84 </a></span> -island of Juan Fernandez, 420 miles off the coast -of Chili, the home for four years of Alexander -Selkirk (to whose adventures we owe Defoe's -creation of Robinson Crusoe), is interesting also -from a botanical point of view. The vegetation of -this oceanic island, 20 square miles in area with -basaltic cliffs rising to a height of 3000 ft. above -the sea, includes more than 40 species of ferns, -eight of which occur nowhere else. One of these -endemic ferns is <i>Thyrsopteris elegans</i>, the only -representative of the genus; it is readily distinguished -by its large and graceful fertile fronds, examples of -which may occasionally be seen on a plant of this -species in the Royal Gardens at Kew: the sporangia -are produced in circular cups which replace the -ordinary leaflets on the lower branches of the frond -and hang from the short axis like miniature clusters -of grapes. It is noteworthy that among the fragmentary -remains of the fern vegetation of the Jurassic -flora in England and in other parts of Europe -specimens occur with fertile segments practically -identical with those of the Juan Fernandez species. -Students of fossil plants are occasionally led away -by the temptation to identify imperfect specimens -with rare existing species to which they exhibit a -superficial resemblance, and this is well illustrated -by the frequent use of the generic name Thyrsopteris -for Jurassic and Lower Cretaceous ferns which are -<span class="pagenum"><a name="Page_85" id="Page_85"> 85 </a></span> -too imperfect to be determined with any degree of -certainty We have, however, satisfactory grounds -for the assertion that the Juan Fernandez fern -affords a striking confirmation of the truth of -Darwin's dictum that 'Rarity, as geology tells us, -is the precursor to extinction.' In this remote oceanic -island, for reasons which we cannot explain, there -lingers an isolated type which belongs to another age.</p> - -<p>The following passage, which forms a fitting -introduction to an account of two other genera of -ancient ferns, is taken from a description of an -ascent of Mount Ophir in the Malay Peninsula by Dr -A. R. Wallace in his well-known book on the Malay -Archipelago:—'After passing a little tangled jungle -and swampy thickets, we emerged into a fine lofty -forest.... We ascended steadily up a moderate slope -for several miles, having a deep ravine on the -left. We then had a level plateau or shoulder to -cross, after which the ascent was steeper and the -forest denser till we came out upon the Padang-Batu, -or stone-field.... We found it to be a steep -slope of even rock, extending along the mountain -side farther than we could see. Parts of it were -quite bare, but where it was cracked and fissured -there grew a most luxuriant vegetation, among which -the pitcher plants were the most remarkable.... A few -coniferae of the genus Dacrydium here first appeared, -and in the thickets, just above the rocky surface, -<span class="pagenum"><a name="Page_86" id="Page_86"> 86 </a></span> -we walked through groves of those splendid ferns, -<i>Dipteris Horsfieldii</i> and <i>Matonia pectinata</i>, which -bear large spreading fronds on slender stems, 6 or -8 feet high'(<a href="#Note_49">49</a>).</p> - -<div class="fig_center" style="width: 358px;"> -<a name="Fig_11"></a> -<img src="images/fig_11.png" width="358" height="360" alt="" /> -<div class="fig_caption">Fig. 11. <i>Matonia pectinata.</i> A group of plants in a wood on -Gunong Tundok, Mount Ophir. (Photograph by Mr A. G. Tansley.)</div> -</div> - -<p><span class="pagenum"><a name="Page_87" id="Page_87"> 87 </a></span></p> - -<p>The two genera Matonia and Dipteris afford -exceptionally striking examples of survivals from -the past. Matonia is represented by two species, -<i>Matonia pectinata</i> (<a href="#Fig_11">Fig. 11</a>), which grows abundantly -on the upper slopes of Padang-Batu in dense thickets -on the rock faces where, as Mr Tansley states, its -associates are a species of Gleichenia, Dipteris, -and a little <i>Pteridium aquilinum</i> (Bracken Fern). -<i>Matonia pectinata</i> occurs also on Bornean mountains -at an altitude of over 3000 ft. and descends to the -coast on some of the Malay islands. The other -species of the genus, <i>Matonia sarmentosa</i>, has so -far been found in one locality only, Niak, Sarawak, -where it was discovered by Mr Charles Hose. -<i>Matonia pectinata</i> has a creeping stem covered with -a thick felt of brown hairs bearing tall fan-shaped -fronds divided into numerous comb-like branches -thickly set with narrow linear leaflets on which -circular clusters of spore-capsules are sparsely scattered. -In some respects Matonia is unlike other -ferns; the fronds constitute a striking feature, and -the anatomy of the stem is still more distinctive. -In the form, development, and arrangement of the -sporangia (spore-capsules)—organs which from the -constancy of their characters have long been recognised -as the most useful basis for classification—Matonia -exhibits distinctive features.</p> - -<p>In order to emphasise the isolated position of the -<span class="pagenum"><a name="Page_88" id="Page_88"> 88 </a></span> -genus it has recently been placed in a separate -family, the Matonineae, of which it is the sole living -representative. The restricted geographical range of -Matonia, considered in connexion with the clearly -marked peculiarities in structure and form, leads us -to expect other evidence in support of the natural -inference that the genus is a survivor of a once -more vigorous and widely spread family. If Matonia -were a recently evolved type which has not spread -far from its original home, we should expect it to -conform more closely than it does to other ferns in -the Malay region. Even assuming for the sake of -argument that variation may occur <i>per saltum</i>, and -new forms may be produced differing in more than -the finer shades of small variation from their parents, -the peculiar features of Matonia are too pronounced -and its individual characteristics too obvious to -warrant the assumption of recent production. It is, -however, from the testimony of the rocks that we -obtain confirmation of the opinion that these Malayan -species are plants on the verge of extinction. In -shales of Jurassic age exposed on the Yorkshire coast -at Gristhorpe Bay and in iron-stained rocks of the -same age between Whitby and Scarborough, well -preserved leaves have been found agreeing in the -shape of the frond, as also in the form of the leaflets -and of the groups of sporangia which they bare, with -those of <i>Matonia pectinata</i>.</p> - -<p><span class="pagenum"><a name="Page_89" id="Page_89"> 89 </a></span></p> - -<p>The exposure by a stroke of the hammer, on the -fractured surface of a rock picked up on the beach -at Hayburn Wyke (a few miles south of Whitby), of -a piece of fern frond which is unmistakably closely -allied to the species described by Wallace on Mount -Ophir, establishes a link between the Jurassic and -the present era and presents a fascinating problem in -geographical distribution. These fossil Matonias are -known to students of ancient plants as species of -the genus Matonidium, a name adopted by a German -botanist for specimens apparently identical with those -from the Yorkshire coast discovered in slightly younger -rocks (Wealden) in North Germany. The same type -has been found also in sediments of Wealden age on -the Sussex coast. Other leaf-impressions agreeing -closely with those of Matonidium have been obtained -from the Yorkshire Jurassic rocks and these are -assigned to another genus Laccopteris, an extinct -member of the family Matonineae. It is not merely -in the habit of the fronds and in the shape and -venation of the leaflets that these fossil ferns resemble -the existing species, but the more important features -exhibited by the spore-capsules supply additional evidence. -It has already been pointed out that the stems -of Matonia are characterised by a type of structure -unknown in an identical form in any other recent fern.</p> - -<p>A few years ago Prof. Bommer discovered fragments -of leaves and stems in Wealden beds a few -<span class="pagenum"><a name="Page_90" id="Page_90"> 90 </a></span> -miles from Brussels sufficiently well preserved to -reveal the details of internal organisation. Some -of these fossils were found to possess structural -features identical with those of the Malayan species -of Matonia. A full account of the fossil representatives -of the Matonia family would be out of place in -a general essay on Links with the Past, but brief -reference may be made to some of the data which -throw light on the geological history of the family. -In strata classed by geologists as Rhaetic, a phase -of earth-history between the Triassic and Jurassic -eras (see <a href="#Page_42">p. 42</a>), species of Laccopteris and allied forms -have been described from several other countries; -from Jurassic and Wealden strata examples of both -Laccopteris and Matonia have been found in Germany, -Portugal, Belgium, Austria, and elsewhere. From -rocks of Cretaceous age, higher in the series than -the Wealden strata, well preserved impressions of -a Matonidium have been discovered in Moravia. -The Matonineae were widely distributed in Europe -during the Rhaetic and Jurassic periods, but, so far -as we know, the family did not survive in the northern -hemisphere beyond the limits of the Cretaceous -period. It is noteworthy that, in spite of the -preservation of the remains of Jurassic and Cretaceous -floras in many extra-European regions, -notably in India, South Africa, Australia, China, and -Tonkin, no specimens have been found which can -<span class="pagenum"><a name="Page_91" id="Page_91"> 91 </a></span> -with confidence be assigned to the Matonineae. A -single fossil has, however, been described from Queensland -which may be a piece of a Laccopteris frond.</p> - -<p>There is some evidence that ferns very similar to -Matonia existed in North America during the Mesozoic -period. It would be in the highest degree rash -to assume that the Matonineae played no part in -the Jurassic vegetation of India, South Africa, and -other southern lands, but there can be little doubt -that the family was especially characteristic of -European floras during a portion of the Mesozoic -era. It would seem that subsequent to the Wealden -period the ancestors of Matonia dwindled in numbers -and their geographical range became much more -restricted.</p> - -<p>The records of Tertiary rocks have hitherto added -nothing to our knowledge of the distribution of the -family subsequent to the Cretaceous period. All -we can say is that the existing species of Matonia -are the last survivors of a family which in the -Jurassic period overspread a wide area in Europe -and probably extended to the other side of the -Atlantic. Exposed to unfavourable climatic conditions -and possibly affected by the revolution in -the plant world consequent on the appearance of -the Flowering Plants, the Matonineae gradually -retreated beyond the equator until the two surviving -species found a last retreat in the Malayan region.</p> - -<p><span class="pagenum"><a name="Page_92" id="Page_92"> 92 </a></span></p> - -<div class="fig_center" style="width: 357px;"> -<a name="Fig_12"></a> -<img src="images/fig_12.png" width="357" height="440" alt="" /> -<div class="fig_caption">Fig. 12. <i>Dipteris conjugata</i> Rein. and, in the middle of the upper -part of the photograph, a frond of <i>Matonia pectinata</i> R. Brown. -Mount Ophir. (Photograph by Mr A. G. Tansley.)</div> -</div> - -<p><span class="pagenum"><a name="Page_93" id="Page_93"> 93 </a></span></p> - -<p>The fern spoken of by Dr Wallace as <i>Dipteris -Horsfieldii</i> (perhaps better known as <i>Dipteris -conjugata</i> (<a href="#Fig_12">Fig. 12</a>)), which grows with <i>Matonia -pectinata</i> on Mount Ophir and in the Malay region -generally, is one of seven species of a genus characterised -by a somewhat wider geographical range -than Matonia. <i>Dipteris conjugata</i> extends to the -Philippines, Samoa, Fiji, New Caledonia, New Guinea -and Central China; its fronds, like those of Matonia, -are borne on long slender stalks attached to a -creeping stem; they have a broad lamina divided by -a deep median sinus into two symmetrical halves and -each half is cut up into segments with a saw-like -edge. Several stout ribs spread through the lamina -from the apex of the long stalk like the open fingers -of a hand; from these ribs smaller veins are given -off at a wide angle, and these in turn give rise to a -reticulum of finer veins forming a skeletal system -like that in the leaves of an oak and many other -flowering plants.</p> - -<p>Numerous groups of spore-capsules are borne on -the lower surface of the broad lobed frond. The -leaves of other species of Dipteris have the same -type of structure, but in some the segmentation of -the lamina is carried further and the leaf consists of -numerous long and narrow segments with one or two -main ribs. Dipteris is represented in the flora -of Assam, and it is interesting to find that a species -<span class="pagenum"><a name="Page_94" id="Page_94"> 94 </a></span> -recently discovered in Borneo is more closely connected -with the Assam type than with those of the -Malay region. Until a few years ago the genus -Dipteris was included in the large family Polypodiaceae -of which nearly all our British ferns are -members, but the discovery of certain distinguishing -features in the structure of the sporangia showed -that these Eastern and Southern species form a -fairly well-defined group worthy of family rank.</p> - -<p>In the Rhaetic plant-beds of Northern and -Central Europe, of North America, Tonkin, and -elsewhere, numerous fossil leaves have been discovered -which in shape, venation, and in the -manner of occurrence of the sporangia bear a close -resemblance to species of Dipteris. Ferns of this -type were abundant in the Jurassic floras of the -northern hemisphere, and it is interesting to find -impressions of Dipteris-like leaves both in the -Jurassic rocks of the Yorkshire coast as well as in -slightly newer beds of the same geological period on -the north-east coast of Sutherland.</p> - -<p>It is impossible to say with confidence how nearly -these Rhaetic and Jurassic ferns were related to the -existing species, as our knowledge of them is less -complete than in the case of the fossil representatives -of the Matonineae, but there can be no reasonable -doubt that in Dipteris as in Matonia we have a connecting -link between the present and a remote past.</p> -<hr class="chap" /> - -<p><span class="pagenum"><a name="Page_95" id="Page_95"> 95 </a></span></p> - - - -<h2><a name="CHAPTER_VI" id="CHAPTER_VI">CHAPTER VI</a></h2> - -<p class="caption3">THE REDWOOD AND MAMMOTH TREES -OF CALIFORNIA</p> - - -<div class="poem"><div class="stanza"> -<span class="i0">'Your sense is sealed, or you should hear them tell<br /></span> -<span class="i1">The tale of their dim life, with all<br /></span> -<span class="i1">Its compost of experience....'<br /></span> -<div class="tdr2 smcap">W. E. Henley.</div> -</div> -</div> - - -<p>Since their introduction into England about the -middle of the nineteenth century, the two Californian -species <i>Sequoia sempervirens</i> (the Redwood) and -<i>Sequoia gigantea</i> (the Mammoth tree) have become -familiar as cultivated trees. The name Sequoia, -said to be taken from Sequoiah, the inventor of the -Cherokee alphabet, was instituted in 1847, while the -name Wellingtonia, often used in horticulture though -discarded by botanists in favour of the older designation -Sequoia, was proposed in 1853. Both species -are now confined to a comparatively small area in -California: their restricted geographical range, considered -as an isolated fact, might be regarded as a -sign of recent origin. The records of the rocks, -however, afford ample proof that rarity in this as in -<span class="pagenum"><a name="Page_96" id="Page_96"> 96 </a></span> -many other instances is the precursor of extinction. -The famous groves of Mariposa and Calaveras -represent the last resting-place of giant survivors -of a race which formerly held its own in Europe and -in other parts of the world.</p> - -<p>The Redwood, <i>Sequoia sempervirens</i>, occupies a -narrow belt of country, rarely more than 20 or 30 -miles from the coast, three hundred miles long from -Monterey in the south to the frontiers of Oregon; -it has a stronger hold on existence than Sequoia -gigantea. In Northern California it still forms pure -forests on the sides of ravines and on the banks of -streams. The tapering trunk, rising from a broad -base to over 300 ft., gives off short horizontal -branches thickly set with narrow spirally disposed -leaves <sup>1</sup>/<sub>4</sub>-<sup>1</sup>/<sub>2</sub> inch in length arranged in two ranks -like the similar leaves of the Yew. The lower -edge of each leaf is decurrent, that is it runs a -short distance down the axis of the branch instead of -terminating at the point of attachment. It is by -paying attention to such details as this as well as to -more important features, that we are able to connect -fragmentary fossil twigs with those of existing -species. The female 'flowers' have the form of -oblong cones from <sup>3</sup>/<sub>4</sub> to 1 inch long: each consists -of a central axis bearing crowded wedge-shaped, -woody appendages or cone-scales, which gradually -increase in breadth towards the exposed distal end -characterised by its four sloping sides and by a -median transverse groove. Several small seeds are -borne on the upper surface of the cone-scales. The -smaller and short-lived male flowers need not be -described.</p> - -<p><span class="pagenum"><a name="Page_97" id="Page_97"> 97 </a></span></p> - -<div class="fig_center" style="width: 367px;"> -<a name="Fig_13"></a> -<img src="images/fig_13.png" width="367" height="481" alt="" /> -<div class="fig_caption">Fig. 13. <i>Sequoia gigantea.</i> King's Co., California. -(From Prof. D. H. Campbell)</div> -</div> - -<p><span class="pagenum"><a name="Page_98" id="Page_98"> 98 </a></span></p> - -<p>The other and better known species <i>Sequoia -gigantea</i> (<a href="#Fig_13">Fig. 13</a>) has an even more restricted range -and is confined to groves on the western slopes of -the Sierra Nevada between 3000 to 9000 ft. above -sea-level.</p> - -<p>This tree is at once distinguished from the -Redwood by its ovate, sharply pointed and stiffer -leaves which retain their spiral disposition and -closely surround the axis of the twigs like obliquely-set -needles. The cones are of the same type as those -of <i>Sequoia sempervirens</i>, but are broader and may -attain a length of 3<sup>1</sup>/<sub>2</sub> inches (95 cm.) (<a href="#Fig_14">Fig. 14</a>).</p> - -<p>Reference has already been made to Sequoia -as a striking illustration of longevity. It is also -selected as an equally impressive example of a type -verging on extinction, which played a prominent part -in the vegetation of both west and east during the -Cretaceous and Tertiary periods.</p> - -<p><span class="pagenum"><a name="Page_99" id="Page_99"> 99 </a></span></p> - -<div class="fig_center" style="width: 359px;"> -<a name="Fig_14"></a> -<img src="images/fig_14.png" width="359" height="682" alt="" /> -<div class="fig_caption">Fig. 14. <i>Sequoia gigantea</i> Torr. (<sup>7</sup>/<sub>8</sub> nat. size.)</div> -</div> - -<p><span class="pagenum"><a name="Page_100" id="Page_100"> 100 </a></span></p> -<p>Scraps of branches with leaves hardly distinguishable -from those of the existing Californian trees -are frequently met with in Tertiary and Mesozoic -sediments, and with them occasionally occur cones -too imperfectly preserved to afford satisfactory -evidence of more than superficial agreement with -those of the recent species. The task of deciphering -the past history of plants, particularly of the Conifers, -is accompanied by many difficulties and insidious -temptations. It is clear from a critical examination -of many of the recorded instances of fossil Sequoias -that the generic name has been frequently used by -writers without adequate grounds. The fragmentary -specimens available to the botanical historian cannot -as a rule be subjected to microscopical investigation, -and even a partial acquaintance with the similarity -of the foliage of different types of living Conifers is -sufficient to convince the student of the need of self-control -in the identification of the fossils. It is, -however, easy to point out obvious pitfalls, though -difficult to maintain a judicial attitude in the -excitement of endeavouring to interpret documents -which are too incomplete to be identified with -certainty. If we put on one side all records of -supposed fossil Sequoias not based on satisfactory -data, there remains a wealth of material testifying to -the antiquity of the surviving species.</p> - -<p>It is by no means improbable that Conifers -closely allied to the Redwoods and Mammoth trees -of California were represented in Jurassic floras; -but hitherto no proof has been obtained of the -occurrence of a Sequoia among the rich material -afforded by the Jurassic plant-beds of Yorkshire -<span class="pagenum"><a name="Page_101" id="Page_101"> 101 </a></span> -and by beds of the same age in other countries. -A small cone has recently been described from -strata near Boulogne belonging to the latest phase -of the Jurassic period, which presents a strong -resemblance in shape and size and in the form of the -cone-scales to those of the recent species. This specimen, -though not conclusive, is the most satisfactory -indication of a Jurassic Sequoia so far discovered. -From Lower Jurassic rocks in Madagascar similar -cones have been recorded in association with foliage-shoots -like those of <i>Sequoia gigantea</i>, but here too -the evidence is not beyond suspicion. In plant-bearing -strata of Wealden age, such as are exposed -in the cliff near Hastings and in deposits of the same -age in North Germany, Portugal, and elsewhere, -twigs and cones have been found which may be -those of trees nearly allied to the genus Sequoia.</p> - -<p><span class="pagenum"><a name="Page_102" id="Page_102"> 102 </a></span></p> - -<div class="fig_center" style="width: 304px;"> -<a name="Fig_15"></a> -<img src="images/fig_15.png" width="304" height="313" alt="" /> -<div class="fig_caption">Fig. 15. <i>Sequoia Couttsiae</i> Heer. Twigs (A) and cone-scales (B) -from Bovey Tracey. (× 3.) (Photographs by Mr and Mrs Clement -Reid.)</div> -</div> - -<p>It is, however, in the sedimentary rocks of -Cretaceous age, rather higher in the series than -those in the Hastings cliffs, and in the succeeding -Tertiary rocks, that undoubted Sequoias are met -with in abundance. At Bovey Tracey in Devonshire -there is a basin-shaped depression in the granitic rocks -of Dartmoor filled with clay, gravel and sand—the -flood-deposits of a Tertiary lake containing waifs and -strays of the vegetation on the surrounding hills. -Among the commonest plants is one to which the -late Oswald Heer gave the name <i>Sequoia Couttsiae</i>, -and his reference of the specimens to the genus -Sequoia has been confirmed by the recent researches -of Air and Mrs Clement Reid(<a href="#Note_50">50</a>). This Tertiary -(Oligocene) species is represented by slender twigs -almost identical with those of <i>Sequoia gigantea</i> and -by well-preserved cone-scales and seeds (<a href="#Fig_15">Fig. 15</a>). -Moreover, it has been possible to examine microscopically -the structure of the carbonised outer skin -of the leaves and to demonstrate its agreement with -that of the superficial tissue in the leaves of the -Mammoth tree. With the Bovey Tracey Sequoia -<span class="pagenum"><a name="Page_103" id="Page_103"> 103 </a></span> -are associated fragments of Magnolia, Vitis, and -<i>Taxodium distichum</i>, the swamp Cypress of North -America, together with other types which have long -ceased to exist in Western Europe. Other British -examples of Sequoia have been described from -Tertiary beds at Bournemouth, the Isle of Wight, -Sheppey, and Antrim, but the material from these -localities is inferior in preservation and cannot be -identified with the same degree of certainty as in the -case of the Devonshire specimens. The occurrence -of twigs and cones of several species of Sequoia in -both Cretaceous and Tertiary rocks in Austria, -Germany, Italy, France, and elsewhere, shows that -the ancestors of the Californian trees were common -in the European region.</p> - -<p>The exploration of Cretaceous and Tertiary rocks -in Arctic Europe has revealed the former existence in -Greenland, Spitzbergen, and other more or less ice-covered -lands of plants which clearly denote a mild -climate. Cones and branches of Sequoias have been -found in abundance in Lower Tertiary beds on Disco -Island off the west coast of Greenland, and similar -evidence of the northern extension of the genus has -been obtained from Spitzbergen. Dr Nathorst of Stockholm -speaks of twigs of Sequoia in the Tertiary clays -of Ellesmere Land almost as perfect as herbarium -specimens. In Tertiary beds on the banks of the -Mackenzie River, in Alaska, Saghalien Island and -<span class="pagenum"><a name="Page_104" id="Page_104"> 104 </a></span> -Vancouver Island, and in Upper Cretaceous rocks in -the Queen Charlotte Islands, remains of Sequoia have -been discovered. One of the most remarkable instances -of the preservation of trees of a bygone age -is supplied by the volcanic deposits of Lower Tertiary -age exposed on the slopes of Amethyst mountain -in the Yellowstone Park district. At different levels -in the volcanic and sedimentary material, which is -piled up to a height of over 2000 ft. above the valley, -as many as fifteen forests are represented by erect -and prostrate limbs of petrified trees (<a href="#Fig_6">Fig. 6</a>). The -microscopical examination of some of these trees -has shown that they bear a striking resemblance to -<i>Sequoia sempervirens</i>. In a photograph of these -petrified forests by the U.S. Geological Survey (36, 2) -one sees living Conifers side by side with the lichen-covered -and weathered trunks of the fossil species -(<i>Sequoia magnifica</i>), living and extinct being at a -distance hardly distinguishable. (Frontispiece.)</p> - -<p>In concluding this brief survey of the fossil records -of Sequoia, reference may be made to the discovery -of petrified wood in Cretaceous rocks in South Nevada, -possessing the anatomical features of <i>Sequoia gigantea</i>, -which shows that close to the present home of the big -trees their ancestors flourished during a period of the -earth's history too remote to be measured by human -reckoning.</p> - -<p>The distribution of the Tertiary and Cretaceous -<span class="pagenum"><a name="Page_105" id="Page_105"> 105 </a></span> -Sequoias would appear to have been mainly in the -northern hemisphere, extending well within the Arctic -circle. It is, however, by no means improbable that -the ancestors of Sequoia flourished far south of the -equator. Reference has been made to Jurassic fossils -from Madagascar which have been compared with the -existing species, and from Lower Tertiary beds in -New Zealand the late Baron Ettingshausen described -some cones and twigs as <i>Sequoia novae zeelandicae</i> -which bear a close resemblance to the existing type. -The available evidence would seem to point to a -northern origin of the genus, though allowance must -be made for erroneous conclusions based on negative -evidence. Further research may well extend the past -distribution of Sequoia in southern lands, but the -data to hand point to the conclusion that the Californian -trees represent the survivors of a type which -flourished in the Cretaceous and Tertiary periods -over a wide area in North America and in what we -now call the Continent of Europe.</p> -<hr class="chap" /> - -<p><span class="pagenum"><a name="Page_106" id="Page_106"> 106 </a></span></p> - - - -<h2><a name="CHAPTER_VII" id="CHAPTER_VII">CHAPTER VII</a></h2> - -<p class="caption3">THE ARAUCARIA FAMILY</p> - -<div class="poem"><div class="stanza"> -<span class="i0">'And so the grandeur of the Forest-tree<br /></span> -<span class="i1">Comes not by casting in a formal mould,<br /></span> -<span class="i1">But from its own divine vitality.'<br /></span> -<div class="tdr2 smcap">Wordsworth.</div> -</div> -</div> - -<p>As an additional illustration of existing cone-bearing -trees which form links with the past we may -briefly consider the genera Araucaria and Agathis, -the two members of the family Araucarieae. It is -generally agreed that the branches of the genealogical -tree of this family extended farther back into the -past than in the case of the majority of Conifers. By -some authors the surviving representatives of the -Araucarian stock are considered to have a strong -claim to be regarded as the most primitive as well as -the oldest of cone-bearing trees, though this opinion, -like many others, is not held by botanists as a whole. -This is not the place to discuss matters of controversy, -and I shall confine myself to a general consideration -of Araucaria and Agathis from the point of view of -their present distribution and the part they played in -<span class="pagenum"><a name="Page_107" id="Page_107"> 107 </a></span> -the vegetation of the Mesozoic and Tertiary epochs. -In 1741 a plant from Amboyna, one of the Moluccas, was -described under the name <i>Dammara alba</i>. For this -tree, known as the Amboyna Fine, the English botanist -Salisbury instituted the generic name Agathis, from a -Greek word (αγαθις) meaning a ball of string and probably -suggested by the form of the cones, which is the -designation usually adopted in botanical literature -instead of the pre-Linnean term Dammara. The best -known species of the genus is the Kauri Pine, probably -the finest forest tree in New Zealand where it still -flourishes from the North Cape to latitude 38° S., -though the occurrence of sub-fossil trunks and pieces -of buried resin shows that the Kauri forests are gradually -dwindling. The stems of this species, <i>Agathis -australis</i>, rise like massive grey columns to a height -of 160 ft., terminating in a succession of spreading -branches given off in tiers from the main trunk. The -thick narrow lanceolate leaves, with several parallel -veins, reach a length of 2 to 3 inches. The female -shoots have the form of small and almost spherical -cones consisting of a central axis bearing overlapping -spiral series of broadly triangular scales (<a href="#Fig_16">Fig. 16</a>). -Each scale carries a single seed with a large wing -attached to one side which facilitates disposal by -wind. Other species of Agathis occur in the Malay -Archipelago, the Philippines, in Queensland, in the -New Hebrides, New Caledonia, the Fiji Islands, and -elsewhere. With the exception of the Australian -Kauri (<i>Agathis robusta</i>), with leaves larger and -broader than those of the New Zealand Kauri, the -genus is essentially an island type. With the exception -of some species of the southern hemisphere -genus Podocarpus, there are no Conifers with foliage -like that of Agathis. It is, however, the broad and thin -single-seeded scales and the spherical cones, in some -species six inches in length, which furnish the most -trustworthy means of identifying the genus.</p> - -<p><span class="pagenum"><a name="Page_108" id="Page_108"> 108 </a></span></p> - -<div class="fig_center" style="width: 668px;"> -<img src="images/fig_16.png" width="668" height="433" alt="" /> -<div class="fig_caption"><p><a name="Fig_16"></a>Fig. 16. A. <i>Agathis robusta</i> Muell. (much reduced). -B. <i>Agathis Moorei</i> Lind. (<sup>1</sup>/<sub>2</sub> nat. size).]</p></div> -</div> - -<div class="fig_center" style="width: 462px;"> -<img src="images/fig_17.png" width="462" height="306" alt="" /> -<div class="fig_caption"><p><a name="Fig_17"></a>Fig. 17. <i>Araucaria excelsa.</i> The upper part of a small tree in the -Cambridge Botanic Garden. (Much reduced.)]</p></div> -</div> - -<p><span class="pagenum"><a name="Page_109" id="Page_109"> 109 </a></span></p> - -<p>The allied genus Araucaria, with the exception -of two South American species, the familiar Monkey -Puzzle, <i>Araucaria imbricata</i>, and a Brazilian tree, -<i>Araucaria brasiliana</i>, is confined within the geographical -area occupied by Agathis. The name Araucaria -was first used by de Jussieu in 1789 for a plant -previously referred to the genus Pinus and described -as one of the most beautiful trees of Chili. This -species, <i>A. imbricata</i>, introduced into England in -1796, grows on the southern slopes of the Andes and, -as in the case of the Kauri forests of New Zealand, -buried stems point to a wider extension of the forests -in earlier days. The sharp and thick leaves of the -Monkey Puzzle distinguish it from all other Conifers; -its large almost spherical seed-bearing cones, more -than half a foot in length, which may occasionally be -seen on well-grown British trees, are unlike those of -other genera. Each of the deep and narrow scales -<span class="pagenum"><a name="Page_110" id="Page_110"> 110 </a></span> -bears a single seed embedded in the substance of the -scale and terminates distally in a narrow upturned -process. Some species of Araucaria, differing considerably -in the form of the leaves and in the shape -and structure of the seed-scales from the Chilian -species, are conveniently placed in a distinct sub-division -of the genus Araucaria. Of this type the -Norfolk Island Pine, <i>Araucaria excelsa</i>, is the best-known -example (<a href="#Fig_17">Fig. 17</a>). It was introduced to Kew -by Sir Joseph Banks in 1793, soon after its discovery -by Captain Cook, who describes the stems of the -<span class="pagenum"><a name="Page_111" id="Page_111"> 111 </a></span> -Norfolk Island trees as resembling basaltic columns, -and relates how on approaching the island everyone -was satisfied that the columnar objects were trees, -'except our Philosophers, who still maintained they -were basaltes.' The leaves are short, about half an -inch long, laterally compressed and slightly spreading -and sickle-shaped—sometimes shorter and broader -and overlapping—arranged in crowded spirals. The -scales of the broadly oval cones are single-seeded, but -differ from those of <i>Araucaria imbricata</i> in having the -seed exposed on the surface and in the greater breadth -and thinner borders of the scales. In both Araucaria -and Agathis the nature of the seed-scales constitutes -a distinguishing feature. The leaves of <i>Araucaria -imbricata</i> differ in form from those of other Conifers. -The foliage shoots of <i>Araucaria excelsa</i> and other -species, <i>e.g.</i> the very closely allied <i>A. Cookii</i> of the -New Hebrides and New Caledonia, though not unlike -the branches of a Japanese Conifer (<i>Cryptomeria -japonica</i>), often cultivated in England, afford fairly -trustworthy characters for identification purposes.</p> - -<p>The minute structure of the wood of both Araucaria -and Agathis constitutes an important distinguishing -feature and enables us to recognise on microscopical -examination even a fragment of wood of either of -these genera. The small elongated cells or water-conducting -elements of the wood of the Araucarieae -are characterised by one or two, and occasionally as -<span class="pagenum"><a name="Page_112" id="Page_112"> 112 </a></span> -many as three or four, contiguous rows of pits on their -radial walls, and these appear in surface view as -flattened circles or polygonal areas.</p> - -<p>These details have been mentioned in order to show -that Araucaria and Agathis are sufficiently distinct -in many respects from other Conifers to render their -identification in a fossil state comparatively easy, at -least much easier than the recognition of the majority -of the members of the Coniferae. It would be going -too far to state definitely that Araucarieae, as defined -by reference to existing species, existed during the -Palaeozoic period; on the other hand it would seem -in a high degree probable that the vegetation of the -Coal age and of the succeeding Permian period included -trees in which certain Araucarian characters -were clearly foreshadowed. The name Araucarioxylon -was formerly applied to petrified wood, obtained from -Palaeozoic as well as from later formations, which -agrees anatomically with that of Araucaria and Agathis. -It has been shown in recent years that much of the -Palaeozoic wood of this type of structure belongs -to the extinct genus Cordaites, a tree which played -a prominent part in the earlier floras. Cordaites -affords a good example of a generalised type: in -its wood-structure it resembles very closely the -existing Araucarieae; its long strap-like leaves are -not unlike those of some species of Agathis; its -male flowers have often been compared with those -<span class="pagenum"><a name="Page_113" id="Page_113"> 113 </a></span> -of the Maiden Hair tree, <i>Ginkgo biloba</i>, and certain -anatomical features form connecting links between -this Palaeozoic genus and the Cycads.</p> - -<p>It is noteworthy that in another Palaeozoic genus, -Walchia, the leaf-bearing branches are identical in appearance -with those of the Norfolk Island Pine (<a href="#Fig_17">Fig. 17</a>) -and some other species of Araucaria. Unfortunately -our knowledge of the reproductive organs of Walchia -is insufficient to warrant any definite statement as to -the degree of consanguinity between this Permian and -Upper Carboniferous plant and the Araucarieae; it -is probable that in Walchia we have a type not far -removed from the line of evolution which led to -Araucaria. Petrified wood, identified as that of -Walchia, and exhibiting the Araucarian type of structure, -has been recorded from Permian rocks of the -Vosges. Other instances might be quoted in support -of the view that the Palaeozoic floras included a few -plants with which the surviving Araucarieae may -fairly claim relationship. Professor Zeiller of Paris -has recently described some fossil shoots from Palaeozoic -rocks in India under the name <i>Araucarites -Oldhami</i> on the ground of the similarity of the leaves -to those of <i>Araucaria imbricata</i>. Similarly, from -Triassic rocks several fossils have been described as -closely allied to Araucaria, in some cases because of -anatomical resemblances and in others on the less -satisfactory evidence furnished by a similarity in the -<span class="pagenum"><a name="Page_114" id="Page_114"> 114 </a></span> -foliage shoots. Professor Jeffrey of Harvard has recently -given an account of a new type of stem -(Woodworthia) from the petrified Triassic forest of -Arizona possessing some Araucarian characters, -though differing from existing species of Araucaria -in certain structural features, a combination of -characters regarded by this Author as an indication -of relationship with the family of Conifers, which -includes the Pines, Firs, Larches and other well-known -northern genera.</p> - -<p>It is, however, from the records of Jurassic rocks -that we obtain the most satisfactory information as to -the great antiquity and the very wide geographical -range of the ancestors of the recent genus. The plant-beds -of the Yorkshire coast afford clear evidence of -the occurrence of Araucarian trees in the woodlands -of the Jurassic period. Petrified wood has been found -at Whitby, associated with jet, showing the minute -structural characteristics of the surviving species of -Araucarieae, and it is not improbable that some at -least of the Whitby jet has been formed from the wood -of Araucarian plants. The carbonised remains of -leafy shoots preserved in the Jurassic shales near -Scarborough and on other parts of the Yorkshire -coast include twigs hardly distinguishable from those -of <i>Araucaria excelsa</i>, though the resemblance of -external form alone, especially in the case of foliage -shoots, does not amount to proof of generic identity. -<span class="pagenum"><a name="Page_115" id="Page_115"> 115 </a></span> -We have, however, the much more trustworthy evidence -of cones and seed-bearing scales in which the -characteristic features of living species are clearly -shown. Seed-bearing scales almost identical with those -of <i>Araucaria excelsa</i> and other recent species have -long been known from the Jurassic rocks of Yorkshire.</p> - -<p>From other parts of England where samples of -Jurassic floras are preserved, as at Stonesfield in -Oxfordshire, in Northamptonshire and elsewhere, -equally striking examples of undoubted Araucarias -have been found.</p> - -<p><a href="#Fig_18">Fig. 18</a> represents part of a large cone described -in 1866 by Mr Carruthers from Jurassic rocks at -Bruton in Somersetshire: this specimen, now in the -British Museum, consists of one side of a spherical -cone about 5 inches long and 5 inches broad; in size, -as in the form of the seed-scales, it shows a striking -likeness to the cones of the Australian species -<i>Araucaria Bidwillii</i>, the Bunya Bunya of Queensland. -Other equally convincing examples of Jurassic -Araucarian cones and seeds may be seen in the -museums of York and Northampton. On the north-east -coast of Sutherland there is a narrow strip of -Jurassic beds forming a low platform between the -granitic and Old Red Sandstone hills and the sea. -From these rocks Hugh Miller described several -fossil plants in his <i>Testimony of the Rocks</i>, and an -examination of a large collection obtained from this -district by the late Dr Marcus Gunn shows that -Miller was justified in speaking of Araucaria as a -member of this northern flora.</p> - -<p><span class="pagenum"><a name="Page_116" id="Page_116"> 116 </a></span></p> - -<div class="fig_center" style="width: 495px;"> -<img src="images/fig_18.png" width="495" height="593" alt="" /> -<div class="fig_caption"><p><a name="Fig_18"></a>Fig. 18. <i>Araucarites sphaerocarpus</i> Carr. From Jurassic rocks at -Bruton, Somersetshire. (British Museum, <sup>2</sup>/<sub>3</sub> nat. size.)]</p></div> -</div> - -<p><span class="pagenum"><a name="Page_117" id="Page_117"> 117 </a></span></p> -<p>There is abundant evidence pointing to the existence -in Britain during the Jurassic period, and in -the early days of the Cretaceous epoch, of Araucarian -trees which differed but slightly from the modern -species confined to the southern hemisphere. In -several localities in France, Germany, and other parts -of the continent, Araucarian fossils have been recognised -in Jurassic rocks. It is almost certain that -some foliage shoots and imperfectly preserved cones -described by Dr Nathorst from Upper Jurassic rocks -in Spitzbergen were borne by a species of Araucaria. -Cone-scales very similar to those from Yorkshire have -been discovered in Wealden beds in Cape Colony, and -Araucarian wood of Jurassic and Cretaceous age has -been found in Madagascar. From Jurassic strata in -India and Victoria (Australia), as well as from Upper -Jurassic and Lower Cretaceous rocks in Virginia and -elsewhere in the eastern United States, well preserved -Araucarian fossils are recorded. In a collection of -Jurassic plants, obtained a few years ago by the -members of a Swedish Antarctic Expedition in -Graham's Land, Dr Nathorst has recognised some -cone-scales of Araucaria, which demonstrate a former -extension of the family beyond the southern limits of -South America.</p> -<p><span class="pagenum"><a name="Page_118" id="Page_118"> 118 </a></span></p> -<p>It is interesting to find that when we ascend higher -in the geological series and pass beyond the Wealden -strata to the Middle and Upper sub-divisions of the -Cretaceous period, evidence of the wide geographical -distribution of the Araucarieae is still abundant. -Araucarian wood has been obtained in rocks classed -as Upper Cretaceous in Egypt, in East Africa, in -Dakota, and elsewhere. In the sedimentary rocks of -the Tertiary period undoubted examples of Araucaria -are less common, though there can be no doubt that -the genus was much more widely spread then than -it is at the present day. The well-known Tertiary -plant-beds of Bournemouth have afforded specimens -of foliage shoots which have been described as a -species of Araucaria, though in the absence of well-preserved -cones or petrified wood we must admit -that the data are inconclusive. It is, however, -legitimate to regard the striking similarity of the -Bournemouth twigs to those of <i>Araucaria excelsa</i> -and <i>A. Cookii</i> as constituting a fairly strong case in -favour of the persistence of Araucaria in Western -Europe up to the earlier stage of the Tertiary period. -Araucarian wood of Tertiary age is recorded from -India, while branches with broad leaves like those -of <i>Araucaria imbricata</i> have been found in Seymour -Island and the Magellan Straits, and specimens -of Tertiary wood are described from Patagonia. -At the other end of the world. Tertiary rocks on the -<span class="pagenum"><a name="Page_119" id="Page_119"> 119 </a></span> -west coast of Greenland have yielded fragments which -may be referred with some hesitation to the genus -Araucaria.</p> - -<p>A few words must be added in regard to the recent -discovery by Professor Jeffrey and Dr Hollick of some -very interesting Cretaceous specimens in New Jersey -of well-preserved cone-scales and foliage shoots of -extinct plants closely related to the existing species -of Agathis(<a href="#Note_51">51</a>). The American fossils are particularly -valuable because their preservation admits of microscopical -examination of the tissues. In Cretaceous -rocks of Staten Island and in other localities on the -eastern border of the northern United States, kite-shaped -seed-bearing scales almost identical in form -with those of recent species of Agathis are fairly -common fossils. Similar specimens have long been -known from Tertiary rocks in western Greenland. -In the case of some of the American examples each -scale bore three seeds instead of a single seed in -living species: on account of this difference Prof. -Jeffrey and Dr Hollick have adopted a distinct -generic name, <i>Protodammara</i>.</p> - -<p>The foregoing sketch is necessarily far from complete, -but it may serve as an illustration of the light -which is thrown on the past history of recent plants -by the investigation of the relics of ancient floras. -The family Araucarieae now represented by a small -number of species which, with the exception of the -<span class="pagenum"><a name="Page_120" id="Page_120"> 120 </a></span> -Andian and Brazilian Araucarias, are restricted to a -small region in the southern hemisphere, was one of -the most widely spread sections of the seed-bearing -plants during the Mesozoic era. Ancestors of Araucaria -must have been common trees in the European -vegetation in Jurassic and Lower Cretaceous periods, -and even as late as the Tertiary period there is evidence -that representatives of the family still lingered in -the north. One conclusion which seems almost unavoidable -is that the species of Araucaria and Agathis -that survive, in some cases only in one or two small -islands in the South Pacific, have in the course of -successive ages wandered from the other end of the -world. Their migrations can be partially traced by -the fragments embedded in Jurassic and later sediments, -but we can only speculate as to the causes -which have contributed to the changes in the fortunes -of the family; how much influence may have been -exerted by changes in physical conditions in the -environment, and to what extent the production of -more successful types may have been the dominant -cause of the decline, it is impossible to say. One -thing at least is certain, that few existing plants are -better entitled to veneration as survivals from the -past than are the living species of Araucaria.</p> -<hr class="chap" /> - -<p><span class="pagenum"><a name="Page_121" id="Page_121"> 121 </a></span></p> - - - -<h2><a name="CHAPTER_VIII" id="CHAPTER_VIII">CHAPTER VIII</a></h2> - -<p class="caption3">THE MAIDEN HAIR TREE</p> - -<div class="poem"><div class="stanza"> -<span class="i0"><span style="margin-left: 12em;">'...the trees</span><br /></span> -<span class="i1">That whisper round a temple become soon<br /></span> -<span class="i1">Dear as the temple's self.'<br /></span> -<br /> -<div class="tdr2 smcap">Keats.</div> -</div> -</div> - -<p>The Maiden Hair tree of China and Japan, which -was introduced into Europe early in the eighteenth -century, has now become fairly well known. Though -hardy in England, it requires warmer summers for -full development and regular flowering. To botanists -this Eastern tree is of peculiar interest, partly -because of the isolated position it occupies in the -plant-kingdom and partly by reason of its great -antiquity. There is probably no other existing tree -which has so strong a claim to be styled a 'living -fossil,' to use a term applied by Darwin to survivals -from the past. In 1712 the traveller Kaempfer -proposed for this plant the generic name Ginkgo, -and Linnaeus adopted this designation, adding the -specific name <i>biloba</i> to denote the bisection of -the wedge-shaped lamina of the leaf into two -<span class="pagenum"><a name="Page_122" id="Page_122"> 122 </a></span> -divergent segments. In 1777 the English botanist -Sir J. E. Smith expressed his disapproval of what -he called the uncouth name Ginkgo by substituting -for <i>Ginkgo biloba</i> the title Salisburia adiantifolia, -but as it is customary to retain names adopted or -proposed by Linnaeus, the founder of the binominal -system of nomenclature, the correct botanical designation -of the maiden hair tree is <i>Ginkgo biloba</i>. -Mere personal preference such as that of Sir J. E. -Smith for Salisburia is not an adequate reason for -rejecting an older name.</p> - -<div class="fig_center" style="width: 485px;"> -<a name="Fig_19"></a> -<img src="images/fig_19.png" width="485" height="511" alt="" /> -<div class="fig_caption">Fig. 19. <i>Ginkgo biloba</i> Linn. (Slightly reduced.)</div> -</div> - -<p><span class="pagenum"><a name="Page_123" id="Page_123"> 123 </a></span></p> - -<p>In its pyramidal habit Ginkgo agrees generally -with the larch and other Conifers. Like the larch -and cedar it possesses two kinds of foliage shoots, -the more rapidly growing long shoots with scattered -leaves and the much shorter dwarf-shoots which -elongate slightly each year and bear several leaves -crowded round their apex. The leaves (<a href="#Fig_19">Fig. 19</a>), -which are shed each year, are similar in the cuneate -form of the lamina and in the fan-like distribution -of the forked veins, to the large leaflets of some -species of maiden hair ferns: the thin lamina carried -by a slender leaf-stalk is usually about 3 inches -across, though in exceptional cases it may reach a -breadth of 8 inches. The lamina is usually divided -by a deep <b>V</b>-shaped sinus into two equal halves; -it may be entire with an irregularly crenulate margin, -or, on seedlings and vigorous long shoots, the lamina -may be cut into several wedge-shaped segments.</p> - -<p>The male and female flowers are borne on separate -trees; the male consists of a central axis giving off -slender branches, each of which ends in a small -<span class="pagenum"><a name="Page_124" id="Page_124"> 124 </a></span> -terminal knot and two elliptical capsules in which -the pollen is produced. The female flowers have -a stouter axis which normally produces two seeds -at the apex. The seed is encased in a green fleshy -substance and, as in the fruit of a cherry or plum, -the kernel is protected by a hard woody shell. In -the form of the leaves and in the structure of the -flowers Ginkgo presents features which clearly distinguish -it from the Conifers, the class in which, -until recently, it was included. In 1896 the Japanese -botanist Hirase made the important discovery that -the male reproductive cells of Ginkgo are large -motile bodies provided with a spirally coiled band -of minute cilia—delicate hairs which by their -rapid lashing-movement propel the cell through -water. In all Flowering Plants and in Conifers the -male reproductive cells have no independent means -of locomotion; they are carried to the female cell -by the formation of a slender tube—the pollen-tube—produced -by the pollen-grain. In the Ferns, Lycopods -and Horsetails—in fact in all members of -the Pteridophyta—as also in the Mosses and Liverworts -as well as in many of the still lower plants, the -male cells swim to the egg by the lashing of cilia -like those on the male cells of Ginkgo. This difference -in regard to the nature of the male cells was considered -to be a fundamental distinction between the -higher seed-bearing plants and all other groups of -<span class="pagenum"><a name="Page_125" id="Page_125"> 125 </a></span> -the vegetable kingdom. It was, therefore, with no -ordinary interest that Hirase's discovery was received, -as it broke down a distinction between the two great -divisions of the plant-world which had been generally -accepted as fundamental; though it is only fair to -say that the German botanist Hofmeister, a man of -exceptional originality and power of grasping the -essential, foresaw the possibility that this arbitrary -barrier would eventually be removed. The Ferns -and other plants in which the male cells are motile, -represent earlier stages in the progress of plant -development, when the presence of water was essential -for the act of fertilisation, a relic of earlier days -when the whole plant-body was fitted for a life in -water. As higher types were produced, the plant-machinery -became less dependent on an aqueous -habitat, and the loss of organs of locomotion in the -male cells is an instance of the kind of change -accompanying the gradual adaptation to life on -land. The idea of the gradual emancipation of plants -from a watery environment is expressed in a somewhat -extreme form by the author of a book entitled -<i>The Lessons of Evolution</i>(<a href="#Note_52">52</a>), who states that the -ocean is the mother of plant-life and that plants -formed the army which conquered the land. In -Ginkgo we have a type which, though similar in -most respects to the Conifers, possesses in its motile -reproductive cells a persistent inheritance from the -<span class="pagenum"><a name="Page_126" id="Page_126"> 126 </a></span> -past. The recognition of this special feature afforded -a sound reason, especially when other peculiarities are -considered, for removing Ginkgo from the Conifers -and instituting a new class-name, Ginkgoales.</p> - -<p>Ginkgo is a generalised type, linked by different -characters both with living members of the two classes -of naked-seeded plants and with certain existing -Palaeozoic genera. It is a survivor of a race which -has narrowly escaped extinction; the last of a long -line that has outlived its family and offers by its persistence -an impressive instance of the past in the -present. Though Mrs Bishop in her <i>Untrodden -Paths in Japan</i> speaks of forests of Maiden Hair -trees apparently in a wild state, it is generally -believed that they were cultivated specimens. -Mr Henry who has an exceptionally wide knowledge -of Chinese vegetation tells us that 'all scientific -travellers in Japan and the leading Japanese botanists -and foresters deny its being indigenous in any part of -Japan; and botanical collectors have not observed it -truly wild in China.' Moreover, Mr E. H. Wilson, -after traversing the whole of the district where -Ginkgo was supposed to occur in a wild state, says -that he found only cultivated trees. There is no reason -to doubt that China is the last stronghold of this -ancient type which in an earlier period of the earth's -history overspread the world.</p> - -<p>A brief summary of the past history of Ginkgo -<span class="pagenum"><a name="Page_127" id="Page_127"> 127 </a></span> -and of the Ginkgoales supplies overwhelming testimony -to the tenacity of life with which the Maiden -Hair tree has persisted through the ages.</p> - -<p>It was pointed out in the account of the past -history of Araucaria that the records obtained from -Palaeozoic rocks, while affording evidence of the -existence of Carboniferous and Permian genera undoubtedly -allied to the living species, do not enable -us to speak with certainty as to the precise degree of -affinity. Similarly, Palaeozoic leaves have been described -as representatives of the class of which Ginkgo -is the sole survivor, but the evidence on which this -relationship is assumed is by no means conclusive.</p> - -<p>The generic name Psygmophyllum has been applied -to some impressions of Ginkgo-like leaves discovered -in the Upper Devonian rocks of Bear Island, a small -remnant of land in the Arctic circle, which has furnished -valuable information as to the composition of -one of the oldest floras of which satisfactory remains -have been found. Other examples of these lobed, -wedge-shaped leaves are recorded from Carboniferous -rocks in Germany, France, and elsewhere; from -Permian strata in the east of Russia and from Palaeozoic -beds in Cape Colony and Kashmir. A relationship -between Psygmophyllum and Ginkgo is, however, by -no means established and rests solely on a resemblance -in the form of the leaves. The close correspondence in -form and venation between some leaves from Permian -<span class="pagenum"><a name="Page_128" id="Page_128"> 128 </a></span> -rocks in the Ural mountains and from Lower Permian -beds in France, and those of the recent species, is -considered by some authors sufficiently striking to -justify the reference of these fossils to the genus -Ginkgo. Similar leaves of Permian age, which may -also be related to the existing species, have been -described under the name Ginkgophyllum. Other -specimens of Palaeozoic age from North America -and elsewhere have been assigned to the Ginkgoales; -but in none of these cases, despite the resemblance -in leaf-form, is there sufficiently convincing evidence -of close relationship to warrant a definite assertion -that the plants in question were members of the -group of which Ginkgo alone remains.</p> - -<p>It is, however, an undoubted fact that the Maiden -Hair tree is connected by a long line of ancestors -with the earliest phase of the Mesozoic era. From -many parts of the world large collections of fossil -plants have been obtained from strata referred to -the Rhaetic period, or to the upper division of the -Triassic system. A comparison of floras from these -geological horizons in different parts of the world -points to a vegetation extending from Australia, -Cape Colony, and South America, to Tonkin, the south -of Sweden and North America, which was characterised -by a greater uniformity than is shown by widely -separated floras at the present day. One of the commonest -genera in Rhaetic floras is that known as -<span class="pagenum"><a name="Page_129" id="Page_129"> 129 </a></span> -Baiera; this name is applied to wedge-shaped leaves -with a slender stalk similar in shape and venation to -those of Ginkgo, but differing in the greater number -and smaller breadth of the segments. Between the -deeply dissected leaf of a typical Baiera with its -narrow linear lobes and the entire or broadly lobed -leaf of a Ginkgo there are many connecting links, and -to some specimens either name might be applied with -equal fitness. Examples of Baiera leaves, in some -cases associated with fragments of reproductive organs, -are recorded from Rhaetic rocks of France, the south -of Sweden, Tonkin, Chili, the Argentine, North America, -South Africa, and from other regions. There is abundant -evidence pointing to the almost world-wide -distribution of the Ginkgoales, as represented more -especially by Baiera, in the older Mesozoic floras. In -the later Jurassic rocks of Yorkshire true Ginkgo -leaves as well as those of the Baiera type are fairly -common; with the leaves have been found pieces -of male and female flowers. Ginkgo and Baiera -have been described from Jurassic rocks of Germany, -France, Russia, Bornholm, and elsewhere in Europe; -they occur abundantly in Middle Jurassic rocks in -northern Siberia, and are represented in the Jurassic -floras of Franz Josef Land, the East Coast of -Greenland, and Spitzbergen (<a href="#Fig_20">Fig. 20</a>). The abundance -of Ginkgo and Baiera leaves associated with -male flowers and seeds discovered in Jurassic rocks, -approximately of the same geological age as those on -the Yorkshire coast, in East Siberia and in the Amur -district, has led to the suggestion that this region -may have been a centre where the Ginkgoales reached -their maximum development in the Mesozoic period.</p> - -<p><span class="pagenum"><a name="Page_130" id="Page_130"> 130 </a></span></p> - -<div class="fig_center" style="width: 494px;"> -<a name="Fig_20"></a> -<img src="images/fig_20.png" width="494" height="470" alt="" /> -<div class="fig_caption">Fig. 20. Fossil Ginkgo leaves. (<sup>1</sup>/<sub>2</sub> nat. size.)</div> - -<table summary="leaves"> -<tr> - <td>A.</td><td class="tdl">Tertiary, Island of Mull.</td> -</tr> -<tr> - <td>B.</td><td class="tdl">Wealden, North Germany (after Schenk).</td> -</tr> -<tr> - <td>C.</td><td class="tdl">Jurassic, Japan (after Yokoyama).</td> -</tr> -<tr> - <td>D.</td><td class="tdl">Jurassic, Australia (after Stirling).</td> -</tr> -<tr> - <td>E.</td><td class="tdl">Jurassic, Siberia (after Heer).</td> -</tr> -<tr> - <td>F.</td><td class="tdl">Jurassic, Turkestan.</td> -</tr> -<tr> - <td>G.</td><td class="tdl">Lower Cretaceous, Greenland (after Heer).</td> -</tr> -<tr> - <td>H.</td><td class="tdl">Jurassic, California (after Fontaine).</td> -</tr> -<tr> - <td>I.</td><td class="tdl">Jurassic, Yorkshire.</td> -</tr> -<tr> - <td>J.</td><td class="tdl">Jurassic, N.E. Scotland (after Stopes).</td> -</tr> -<tr> - <td>K.</td><td class="tdl">Wealden, Franz Josef Land (after Nathorst).</td> -</tr> -<tr> - <td>L.</td><td class="tdl">Rhaetic, South Africa.</td> -</tr> -<tr> - <td>M.</td><td class="tdl">Jurassic, Spitzbergen (after Heer).</td> -</tr> -</table> -</div> - - -<p><span class="pagenum"><a name="Page_131" id="Page_131"> 131 </a></span></p> - -<p>It should be added that other genera of Jurassic -and Rhaetic fossils in addition to Ginkgo and Baiera -have been referred to the Ginkgoales, though evidence -of such affinity is not convincing. There is, however, -good reason to believe that this widespread group -was represented by several genera in the older Mesozoic -floras.</p> - -<p>The occurrence of the Ginkgoales in Jurassic rocks -in King Charles Land and in the New Siberian Islands -(lat. 78° and 75° N.), in Central China, Japan, -Turkestan, California, Oregon, South Africa, Australia, -and Graham's Land demonstrates the cosmopolitan -nature of the group. During the later part of the -Jurassic period and in the Wealden floras both Baiera -and Ginkgo were abundant; leaves are recorded from -Jurassic strata in the north-east of Scotland, from -Lower Cretaceous or Wealden rocks in North Germany, -Portugal, Vancouver Island, Wyoming, and Greenland.</p> - -<p>During the Tertiary period, or probably in the -earlier days of that era. Ginkgo flourished in North -America, in Alaska and in the Mackenzie River district, -Greenland, Saghalien Island, and in several European -regions. In <a href="#CHAPTER_III">Chapter III</a> reference was made to the -<span class="pagenum"><a name="Page_132" id="Page_132"> 132 </a></span> -volcanic activity which characterised the north-west -European area in the early Tertiary period and resulted -in the formation of the thick sheets of basalt on the -north-east coast of Ireland and in the Inner Hebrides. -There were occasional pauses in the volcanic activity, -during which vegetation established itself on the -weathered surface of the lava, and left traces of its -existence in the leaves and twigs preserved in the -sedimentary material enclosed between successive -lava-floras. At Ardtun Head in the Isle of Mull -beautifully preserved leaves of Ginkgo, 2-4 inches -in breadth, with the median sinus and the venation -characteristic of the leaves of the existing plant, have -been discovered in a bed of clay which marks the site -of a lake in a depression on the lava-plateau. The -resemblance of these Tertiary leaves from Mull to -those of the surviving Maiden Hair tree is so close as -to suggest specific identity. Mr Starkie Gardner and -Baron Ettingshausen have described some seeds from -the London clay (Lower Tertiary) in the Isle of Sheppey -as those of Ginkgo, but this identification rests on -data too insufficient to be accepted without hesitation.</p> - -<p>The recent cultivation of <i>Ginkgo biloba</i> in Britain -may therefore be spoken of as the re-introduction of -a plant which in the earlier part or in the middle of -the Tertiary period flourished in the west of Scotland, -and was abundant in England in the earlier Jurassic -period. It is impossible to say with any confidence -where the Ginkgoales first made their appearance -<span class="pagenum"><a name="Page_133" id="Page_133"> 133 </a></span>, -whether in the far north or in the south, nor are we -able to explain the gradual decline of so venerable -and vigorous a race.</p> - -<p>As we search among the fragmentary herbaria -scattered through the sedimentary rocks in that comparatively -small portion of the earth's crust which is -accessible to investigation, we discover evidence of -a shifting of the balance of power among different -classes of plants in the course of our survey of successive -floras. Plants now insignificant and few in -number are found to be descendants of a long line of -ancestors stretching back to a remote antiquity when -they formed the dominant class. Others which flourished -in a former period no longer survive, either -themselves or in direct descendants. 'The extinction -of species has been involved in the most gratuitous -mystery.' We can only speculate vaguely as to the -cause of success or failure. Certain types were better -armed for the struggle for life, and produced descendants -able to hold their own and to perpetuate -the race through the ages in an unbroken line. -Others had a shorter life and fell out of the ranks of -the advancing and ever changing army. To quote -Darwin's words:'We need not marvel at extinction; -if we must marvel, let it be at our own presumption -in imagining for a moment that we understand the -many complex contingencies on which the existence -of each species depends.'</p> -<hr class="chap" /> - -<p><span class="pagenum"><a name="Page_134" id="Page_134"> 134 </a></span></p> - - - -<h2><a name="BIBLIOGRAPHY" id="BIBLIOGRAPHY">BIBLIOGRAPHY</a></h2> - - -<p>Many of the books and papers dealing with subjects touched -upon in this volume are not included in the following list. For -reference to a more complete bibliography the reader should -consult more technical treatises.</p> - -<div class="blockquot"> - -<p><a name="Note_1">1.</a> <span class="smcap">Holmes, T. Rice.</span> Ancient Britain and the invasions of -Julius Caesar. Oxford, 1907.</p> - -<p><a name="Note_2">2.</a> <span class="smcap">Mitchell, A.</span> The Past in the Present; what is Civilisation? -Edinburgh, 1880.</p> - -<p><a name="Note_3">3.</a> <span class="smcap">Weismann, A.</span> Essays upon Heredity and Kindred Biological -Problems, (<span class="smcap">I.</span> The Duration of Life.) Vol. <span class="smcap">I</span>. -Edited by E. B. Poulton, S. Schnland, and A. E. -Shipley. (Second Edition.) Oxford, 1891.</p> - -<p><a name="Note_4">4.</a> <span class="smcap">The Historie of the World</span>, commonly called the Naturall -Historic of the <span class="smcap">C. Plinius Secundus</span>. Translated into -English by Philemon Holland. London, 1634.</p> - -<p><a name="Note_5">5.</a> <span class="smcap">Hooker, J. D.</span> On Three Oaks of Palestine. <i>Trans. -Linnean Society</i>, Vol. <span class="smcap">XXIII</span>. p. 381. 1862.</p> - -<p><a name="Note_6">6.</a> <span class="smcap">Holtermann, Carl.</span> Der Einfluss des Klimas auf den Bau -der Pflanzengewebe. Leipzig, 1907.</p> - -<p><a name="Note_7">7.</a> <span class="smcap">Atkinson, A.</span> Notes on an Ancient Boat found at Brigg. -<i>Archaeologia</i>, Vol. <span class="smcap">I</span>. p. 361. 1887.</p> - -<p><a name="Note_8">8.</a> <span class="smcap">Huxley, T. H.</span> Man's Place in Nature and other Anthropological -Essays. <i>Collected Essays</i>, Vol. <span class="smcap">VII</span>. (On the -methods and results of Ethnology.) London, 1901.</p> - -<p><a name="Note_9">9.</a> <span class="smcap">Lewis, F. J.</span> The sequence of Plant Remains in the British -Peat Mosses. <i>Science Progress</i>, No. 6. October, 1907.</p> - -<p><span class="pagenum"><a name="Page_135" id="Page_135"> 135 </a></span></p> - -<p><a name="Note_10">10.</a> <span class="smcap">Strahan, A.</span> On submerged Land-surfaces at Barry, -Glamorganshire. With notes on the Fauna and Flora -by Clement Reid; etc. <i>Quart. Journ. Geological -Society</i>, Vol. <span class="smcap">LII</span>. p. 474. 1896.</p> - -<p><a name="Note_11">11.</a> <span class="smcap">The Life and Letters of Charles Darwin.</span> Edited by -Francis Darwin. 3 Vols. London, 1887.</p> - -<p><a name="Note_12">12.</a> <span class="smcap">More Letters of Charles Darwin.</span> Edited by Francis -Darwin and A. C. Seward. 2 Vols. London, 1903.</p> - -<p><a name="Note_13">13.</a> <span class="smcap">Ward, Lester F.</span> The Course of Biologic Evolution. -Anniversary Address of the President of the Biological -Society. Washington, 1890.</p> - -<p><a name="Note_14">14.</a> <span class="smcap">Marshall, W.</span> <i>Anacharis alsinastrum</i>, a new water weed. -(Reprinted from the Cambridge <i>Independent Press</i>.) -London, 1852.</p></div> - -<div class="tdl"> -<table summary="list"> -<tr> - <td rowspan="2"><a name="Note_15">15.</a></td> - <td rowspan="2"><img src="images/bracel_116.png" width="11" height="116" alt="{" /></td> - <td class="tdl"><span class="smcap">Bailey, C.</span> Notes on the structure, the occurrence in - Lancashire, and the source of origin, of <i>Naias gramineus</i> - Delile, var. <i>Delilei magnus</i>. <i>Journal of Botany</i>, - Vol. <span class="smcap">XXII</span>. p. 305. 1884.</td> -</tr> -<tr> - <td class="tdl"><span class="smcap">Weiss, F. H.</span> and <span class="smcap">H. Murray</span>. On the occurrence and - distribution of some alien aquatic plants in the Reddish - Canal. <i>Mem. Proc. Manchester Lit. and Phil. Society</i>, - Vol. <span class="smcap">LIII</span>. Pt. <span class="smcap">II</span>. 1909.</td> -</tr> -</table> -</div> - -<div class="blockquot"> - -<p><a name="Note_16">16.</a> <span class="smcap">Bennett, A.</span> The Halifax Potamogeton. <i>Naturalist</i>, -No. 621. October, 1908.</p> - -<p><a name="Note_17">17.</a> <span class="smcap">Hooker, J. D.</span> Outlines of the Distribution of Arctic -Plants. <i>Trans. Linn. Soc.</i> Vol. <span class="smcap">XXIII</span>. p. 251. 1862.</p> - -<p><a name="Note_18">18.</a> <span class="smcap">Engler, A.</span> Plants of the Northern Temperate Zone in -their transition to the High Mountains of Tropical -Africa. <i>Annals of Botany</i>, Vol. <span class="smcap">XVIII</span>. p. 523. 1904.</p> - -<p><a name="Note_19">19.</a> <span class="smcap">Darwin, C.</span> The Origin of Species. London, 1900.</p> - -<p><a name="Note_20">20.</a> <span class="smcap">Ridley, H. N.</span> On the dispersal of seeds by wind. <i>Annals -of Botany</i>, Vol. <span class="smcap">XIX</span>. p. 351. 1905.</p> - -<p><a name="Note_21">21.</a> <span class="smcap">Hooker, J. D.</span> On the Cedars of Lebanon, Taunus, Algeria, -and India. <i>The Natural History Review</i>, 1862, p. 11.</p> - -<p><span class="pagenum"><a name="Page_136" id="Page_136"> 136 </a></span></p> - -<p><a name="Note_22">22.</a> <span class="smcap">Forbes, E.</span> On the connection between the distribution -of the existing Fauna and Flora of the British Isles, -and the geological changes which have affected their -area.... <i>Memoirs, Geological Survey</i>, Vol. <span class="smcap">I</span>. p. 336. -1846.</p> - -<p><a name="Note_23">23.</a> <span class="smcap">Praeger, R. L.</span> The Wild Flowers of the West of Ireland -and their history. <i>Journ. R. Hort. Soc.</i> Vol. <span class="smcap">XXXVI</span>. -p. 299. 1910.</p> - -<p><a name="Note_24">24.</a> <span class="smcap">Ernst, A.</span> The New Flora of the Volcanic Island of -Krakatau. Translated by A. C. Seward. Cambridge, -1908.</p> - -<p><a name="Note_25">25.</a> <span class="smcap">Praeger, R. L.</span> A Tourist's Flora of the West of Ireland. -Dublin, 1909.</p></div> - -<div class="tdl"> -<table summary="list"> -<tr> - <td rowspan="2"><a name="Note_26">26.</a></td> - <td rowspan="2"><img src="images/bracel_86.png" width="14" height="86" alt="{" /></td> - <td class="tdl"><span class="smcap">Rendle, A. B.</span> <i>Sisyrinchium californicum</i> Dryand. -<i>Journal of Botany</i>, Vol <span class="smcap">XXXIV</span>. p. 494. 1896.</td> -</tr> -<tr> - <td class="tdl"><span class="smcap">Marshall, E. S.</span> <i>Sisyrinchium californicum</i> in Ireland. - <i>Ibid.</i> p. 366.</td> -</tr> -</table> -</div> - -<div class="tdl"> -<table summary="list"> -<tr> - <td rowspan="2"><a name="Note_27">27.</a></td> - <td rowspan="2"><img src="images/bracel_86.png" width="14" height="86" alt="{" /></td> - <td class="tdl"><span class="smcap">Reid, Clement.</span> The Origin of the British Flora. London, 1899.</td> -</tr> -<tr> - <td class="tdl"><span class="smcap">Reid, Clement</span> and <span class="smcap">Eleanor M.</span> On the Pre-glacial - Flora of Britain <i>Journ. Linn. Soc.</i> Vol. <span class="smcap">XXVIII</span>. p. 206. - 1908.</td> -</tr> -</table> -</div> - -<div class="blockquot"> - -<p><a name="Note_28">28.</a> <span class="smcap">Lankester, Sir Edwin Ray.</span> Mature and Man. The -Romanes Lecture. Oxford, 1905.</p> - -<p><a name="Note_29">29.</a> <span class="smcap">Huxley, T. H.</span> On a Piece of Chalk. <i>Collected Essays</i>, -Vol. <span class="smcap">VIII</span>. London, 1896.</p> - -<p><a name="Note_30">30.</a> <span class="smcap">Jukes-Browne, A. J.</span> The Building of the British Isles. -London, 1911.</p> - -<p><a name="Note_31">31.</a> <span class="smcap">Ray, J.</span> Three Physico-Theological Discourses, etc. (2nd -Edition.) London, 1693.</p> - -<p><a name="Note_32">32.</a> <span class="smcap">Woodward, J.</span> An Essay toward a Natural History of -the Earth. London, 1695.</p> - -<p><a name="Note_33">33.</a> <span class="smcap">Sollas, W. J.</span> The Age of the Earth, and other geological -studies. London, 1905.</p> - -<p><span class="pagenum"><a name="Page_137" id="Page_137"> 137 </a></span></p> - -<p><a name="Note_34">34.</a> <span class="smcap">Ward, L. F.</span> Status of the Mesozoic Floras of the United -States. <i>Monograph 48, U. S. Geol. Surv.</i> 1905.</p> - -<p><a name="Note_35">35.</a> <span class="smcap">Arber, E. A. Newell.</span> <i>Cupressinoxylon Hookeri</i> sp. nov., -a large silicified tree from Tasmania. <i>Geological Magazine</i>, -Vol. <span class="smcap">I</span>. [<span class="smcap">V.</span>], p. 7. 1904.</p></div> - -<div class="tdl"> -<table summary="list"> -<tr> - <td rowspan="2"><a name="Note_36">36.</a></td> - <td rowspan="2"><img src="images/bracel_86.png" width="14" height="86" alt="{" /></td> - <td class="vtop">1.</td> - <td class="tdl vtop"><span class="smcap">Holmes, W. H.</span> Fossil Forests of the Volcanic Tertiary - Formations of the Yellowstone National Park. Ann. - Rep. Geol. and Geogr. Surv. (U.S.A.), 1878, Pt. <span class="smcap">II</span>. p. 47.</td> -</tr> -<tr> - <td class="vtop">2.</td> - <td class="tdl vtop"><span class="smcap">Knowlton, F. H.</span> Fossil Flora of the Yellowstone - National Park. <i>Monograph 32, U. S. Geol. Survey</i>, - Pt. <span class="smcap">II</span>. 1899.</td> -</tr> -</table> -</div> - -<div class="blockquot"> - -<p><a name="Note_37">37.</a> <span class="smcap">Darwin, C.</span> Journal of Researches into the Natural History -and Geology of the countries visited during the voyage -round the world of H.M.S. 'Beagle.' London, 1902.</p> - -<p><a name="Note_38">38.</a> <span class="smcap">Dufferin, Lord.</span> Letters from High Latitudes. London. -<span class="smcap">N.D.</span></p> - -<p><a name="Note_39">39.</a> <span class="smcap">Amundsen, R.</span> The North-West Passage. 2 Vols. London,. -1908.</p> - -<p><a name="Note_40">40.</a> <span class="smcap">MacDougal, D. T.</span> Botanical Explorations in the South-west. -<i>Journ. New York Botanical Garden</i>, Vol. <span class="smcap">V</span>. -p. 89. 1904.</p></div> - -<div class="tdl"> -<table style="width: 100%;" summary="list"> -<tr> - <td rowspan="2"><a name="Note_41">41.</a></td> - <td rowspan="2"><img src="images/bracel_60.png" width="11" height="60" alt="{" /></td> - <td class="tdl"><span class="smcap">Goeppert, H. R.</span> and <span class="smcap">A. Menge.</span> Die Flora des Bernsteins. - Danzig, 1883.</td> -</tr> -<tr> - <td class="tdl"><span class="smcap">Conwentz, H.</span> Monographie der baltischen Bernsteinbume. Danzig, 1890.</td> -</tr> -</table> -</div> - -<div class="blockquot"> - -<p><a name="Note_42">42.</a> <span class="smcap">Hovelacque, M.</span> Sur la Nature vgtale de l'<i>Aachenosaurus -multidens.</i> <i>Bull. Soc. Belge de Gol.</i> etc. Tome <span class="smcap">IV</span>. -p. 59. 1890.</p> - -<p><a name="Note_43">43.</a> <span class="smcap">Oliver, F. W.</span> and <span class="smcap">D. H. Scott</span>. On the structure of the -Palaeozoic seed <i>Lagenostoma Lomaxi</i>. <i>Phil. Trans. -R. Soc.</i> Vol. <span class="smcap">CXCVII</span>. p. 193. 1904.</p> - -<p><a name="Note_44">44.</a> <span class="smcap">Kidston, R.</span> On the fructification of <i>Neuropteris heterophylla</i>. -<i>Phil. Trans. Royal Soc. London</i>, Vol. <span class="smcap">CXCVII</span>. p. 1.</p> -<span class="pagenum"><a name="Page_138" id="Page_138"> 138 </a></span> -<p><a name="Note_45">45.</a> <span class="smcap">Smith, Geoffrey.</span> A Naturalist in Tasmania. Oxford, 1909.</p> - -<p><a name="Note_46">46.</a> <span class="smcap">Campbell, D. H.</span> On the Distribution of the Hepaticae, -and its significance. <i>New Phytologist</i>, Vol. <span class="smcap">VI</span>. p. -203. 1907.</p> - -<p><a name="Note_47">47.</a> <span class="smcap">Kidston, R.</span> and <span class="smcap">D. T. Gwynne-Vaughan</span>. On the -Fossil Osmundaceae. <span class="smcap">Phil. Trans. R. Soc. Edinburgh</span>, -Vols. <span class="smcap">XLV., XLVI.</span> 1907-09.</p> - -<p><a name="Note_48">48.</a> <span class="smcap">Seward, A. C.</span> Fossil Plants. 2 Vols. Cambridge, -1898-1910.</p> - -<p><a name="Note_49">49.</a> <span class="smcap">Wallace, A. R.</span> The Malay Archipelago. London, 1886.</p> - -<p><a name="Note_50">50.</a> <span class="smcap">Reid, C.</span> and <span class="smcap">Eleanor M.</span> The Lignite of Bovey -Tracey. <i>Phil. Trans. Royal Soc. London</i>, Vol. 201, p. 161. 1910.</p> - -<p><a name="Note_51">51.</a> <span class="smcap">Hollick, A.</span> and <span class="smcap">E. C. Jeffrey</span>. Studies of -Cretaceous Coniferous remains from Kreischerville, New York. -<i>Mem. New York Bot. Garden</i>, Vol. <span class="smcap">III</span>. 1909.</p> - -<p><a name="Note_52">52.</a> <span class="smcap">Hutton, F. W.</span> The Lessons of Evolution. London, 1902.</p></div> -<hr class="chap" /> - -<p><span class="pagenum"><a name="Page_139" id="Page_139"> 139 </a></span></p> - - - -<h2><a name="INDEX" id="INDEX">INDEX</a></h2> - - -<p class="p0"> -<i>Aachenosaurus multidens</i>, <a href="#Page_68">68</a><br /> -<i>Agathis australis</i>, <a href="#Page_107">107</a><br /> -<i>A. Moorei</i>, <a href="#Page_108">108</a><br /> -<i>A. robusta</i>, <a href="#Page_108">108</a>, <a href="#Page_109">109</a><br /> -Amber, <a href="#Page_65">65</a>, <a href="#Page_66">66</a><br /> -Amethyst Mountain, <a href="#Page_59">59</a>, <a href="#Page_60">60</a>, <a href="#Page_104">104</a><br /> -Amundsen, E., <a href="#Page_62">62</a><br /> -<i>Anacharis alsinastrum</i>, <a href="#Page_20">20</a><br /> -<a id="Angiosperms"></a>Angiosperms, history of, <a href="#Page_16">16</a>, <a href="#Page_53">53</a>, <a href="#Page_69">69</a>, <a href="#Page_70">70</a><br /> -Annual rings, <a href="#Page_5">5-9</a><br /> -Antarctic fossil plants, <a href="#Page_70">70</a>, <a href="#Page_117">117</a><br /> -<i>Araucaria Bidwillii</i>, <a href="#Page_115">115</a><br /> -<i>A. brasiliana</i>, <a href="#Page_109">109</a><br /> -<i>A. Cookii</i>, <a href="#Page_111">111</a>, <a href="#Page_118">118</a><br /> -<a id="A_excelsa"></a><i>A. excelsa</i>, <a href="#Page_110">110</a>, <a href="#Page_111">111</a>, <a href="#Page_114">114</a>, <a href="#Page_115">115</a>, <a href="#Page_118">118</a><br /> -<i>A. imbricata</i>, <a href="#Page_109">109</a>, <a href="#Page_111">111</a>, <a href="#Page_113">113</a>, <a href="#Page_118">118</a><br /> -Araucarieae, <a href="#Page_106">106-120</a><br /> -Araucarioxylon, <a href="#Page_112">112</a><br /> -<i>Araucarites Oldhami</i>, <a href="#Page_113">113</a><br /> -<i>A. sphaerocarpus</i>, <a href="#Page_116">116</a><br /> -Arbutus Unedo, <a href="#Page_31">31-33</a>, <a href="#Page_36">36</a><br /> -Archaean rocks, <a href="#Page_43">43</a><br /> -Arctic plants, <a href="#Page_22">22</a>, <a href="#Page_23">23</a>, <a href="#Page_30">30</a>, <a href="#Page_69">69</a>, <a href="#Page_127">127</a><br /> -Arctic-Alpine plants, <a href="#Page_22">22</a>, <a href="#Page_23">23</a><br /> -Arizona, fossil forests of, <a href="#Page_59">59</a><br /> -Artocarpus, <a href="#Page_28">28</a>, <a href="#Page_29">29</a><br /> -<br /> -Baiera, <a href="#Page_129">129</a>, <a href="#Page_131">131</a><br /> -Banks, Sir Joseph, <a href="#Page_110">110</a><br /> -Barry, forest beds at, <a href="#Page_13">13</a><br /> -Bennett, A., <a href="#Page_21">21</a><br /> -<i>Bidens tripartita</i>, <a href="#Page_46">46</a>, <a href="#Page_47">47</a><br /> -Bishop, Mrs, <a href="#Page_126">126</a><br /> -Bommer, C, <a href="#Page_73">73</a>, <a href="#Page_82">82</a>, <a href="#Page_89">89</a><br /> -Bovey Tracey, fossil plants from, <a href="#Page_101">101-103</a><br /> -Bower, Prof., <a href="#Page_73">73</a><br /> -Bracken Fern, <a href="#Page_75">75</a>, <a href="#Page_77">77</a>, <a href="#Page_83">83</a>, <a href="#Page_87">87</a><br /> -Brandon, flint-knappers of, <a href="#Page_3">3</a><br /> -Brigg, dug-out boat from, <a href="#Page_10">10</a>, <a href="#Page_11">11</a><br /> -British flora, <a href="#Page_19">19-38</a><br /> -<br /> -<i>Caltha palustris</i>, <a href="#Page_47">47</a><br /> -Campbell, Prof. D. H., <a href="#Page_79">79</a><br /> -Candolle, A. P. de, <a href="#Page_7">7</a>, <a href="#Page_33">33</a><br /> -Canton, W., <a href="#Page_34">34</a><br /> -Carboniferous plants, <a href="#Page_66">66-68</a>, <a href="#Page_72">72-75</a>, <a href="#Page_127">127</a><br /> -Carruthers, Dr W., <a href="#Page_115">115</a><br /> -Cedars, <a href="#Page_27">27</a><br /> -Cheddar Pink, <a href="#Page_24">24</a><br /> -<i>Cinnamomum prototypum</i>, <a href="#Page_65">65</a>, <a href="#Page_66">66</a><br /> -Climate, fossil plants and, <a href="#Page_68">68</a>, <a href="#Page_69">69</a><br /> -Coal age, plants of the, <a href="#Page_19">19</a>, <a href="#Page_66">66</a>, <a href="#Page_67">67</a><br /> -Connemara, <a href="#Page_30">30</a>, <a href="#Page_31">31</a><br /> -Cook, Capt., <a href="#Page_111">111</a><br /> -Coral polyps compared with plants, <a href="#Page_8">8</a><br /> -Cordaites, <a href="#Page_112">112</a><br /> -Cornwall, Pyrenean Heaths in, <a href="#Page_31">31</a><br /> -<span class="pagenum"><a name="Page_140" id="Page_140"> 140 </a></span>Cretaceous plants, <a href="#Page_16">16</a>, <a href="#Page_17">17</a>, <a href="#Page_53">53</a>, <a href="#Page_82">82</a>, <a href="#Page_117">117</a><br /> -Cromer Forest bed, <a href="#Page_48">48</a><br /> -<i>Cryptomeria japonica</i>, <a href="#Page_111">111</a><br /> -Cycads, <a href="#Page_11">11</a>, <a href="#Page_72">72-74</a><br /> -<br /> -<i>Daboecia polifolia</i>, <a href="#Page_30">30</a><br /> -Dacrydium, <a href="#Page_85">85</a><br /> -Dakota group, flora of, <a href="#Page_17">17</a><br /> -<i>Dammara alba</i>, <a href="#Page_107">107</a><br /> -Darwin, C, <a href="#Page_16">16</a>, <a href="#Page_24">24</a>, <a href="#Page_25">25</a>, <a href="#Page_33">33</a>, <a href="#Page_39">39</a>, <a href="#Page_40">40</a>, <a href="#Page_61">61</a>, <a href="#Page_133">133</a><br /> -Devonshire, Pyrenean Heaths in, <a href="#Page_31">31</a><br /> -<i>Dianthus caesius</i>, <a href="#Page_24">24</a><br /> -Dipteris, <a href="#Page_77">77</a>, <a href="#Page_92">92-94</a><br /> -<i>D. conjugata</i>, <a href="#Page_92">92</a>, <a href="#Page_93">93</a><br /> -<i>D. Horsfieldii</i>, <a href="#Page_86">86</a>, <a href="#Page_93">93</a><br /> -Disco Island, Fossil plants from, <a href="#Page_28">28</a>, <a href="#Page_69">69</a>, <a href="#Page_82">82</a>, <a href="#Page_103">103</a><br /> -Discontinuous distribution, <a href="#Page_26">26</a><br /> -Dispersal of plants, rate of, <a href="#Page_25">25</a>, <a href="#Page_26">26</a><br /> -Distribution of plants, <a href="#Page_15">15-38</a><br /> -Drift-wood, <a href="#Page_61">61-63</a><br /> -<i>Dryas octopetala</i>, <a href="#Page_22">22</a><br /> -Dufferin, Lord, <a href="#Page_61">61</a><br /> -<br /> -<i>Elodea canadensis</i>, <a href="#Page_20">20</a>, <a href="#Page_21">21</a><br /> -Engler, Prof., <a href="#Page_23">23</a><br /> -<i>Erica ciliaris</i>, <a href="#Page_31">31</a><br /> -<i>E. Mackaii</i>, <a href="#Page_31">31</a><br /> -<i>E. mediterranea</i>, <a href="#Page_30">30</a>, <a href="#Page_31">31</a><br /> -<i>E. vagans</i>, <a href="#Page_31">31</a><br /> -<i>Eriocaulon septangulare</i>, <a href="#Page_35">35-38</a><br /> -Ettingshausen, Baron, <a href="#Page_105">105</a>, <a href="#Page_132">132</a><br /> -<br /> -Ferns, <a href="#Page_71">71-94</a><br /> -Flowering plants, see <a href="#Angiosperms">Angiosperms</a><br /> -Forbes, E., <a href="#Page_31">31-34</a>, <a href="#Page_37">37</a><br /> -Fossil plants, as thermometers, <a href="#Page_68">68</a>;<br /> -<span style="margin-left: 1em;">preservation of, <a href="#Page_56">56-70</a></span><br /> -<br /> -Gardner, J. S., <a href="#Page_132">132</a><br /> -Geographical distribution of plants, <a href="#Page_15">15-38</a><br /> -Geological evolution of Britain, <a href="#Page_29">29</a><br /> -Geological record, <a href="#Page_39">39-55</a><br /> -Geological table, <a href="#Page_42">42</a>, <a href="#Page_43">43</a><br /> -Geological time, <a href="#Page_2">2</a>, <a href="#Page_3">3</a>, <a href="#Page_49">49</a><br /> -<i>Ginkgo biloba</i>, <a href="#Page_113">113</a>, <a href="#Page_120">120-133</a><br /> -Ginkgoales, <a href="#Page_18">18</a>, <a href="#Page_120">120-133</a><br /> -Ginkgophyllum, <a href="#Page_128">128</a><br /> -Glacial period, effect on vegetation of, <a href="#Page_29">29-32</a>, <a href="#Page_45">45</a>, <a href="#Page_47">47</a><br /> -<i>Gladiolus illyricus</i>, <a href="#Page_31">31</a><br /> -Gleichenia, <a href="#Page_81">81-83</a><br /> -Graham's Land, <a href="#Page_70">70</a>, <a href="#Page_117">117</a><br /> -Gunn, Dr Marcus, <a href="#Page_117">117</a><br /> -Gwynne-Vaughan, Prof., <a href="#Page_80">80</a><br /> -Gymnosperms, <a href="#Page_17">17</a>, <a href="#Page_18">18</a><br /> -<br /> -<i>Habenaria intacta</i>, <a href="#Page_37">37</a><br /> -Halifax, plants from canal near, <a href="#Page_21">21</a><br /> -Heer, O., <a href="#Page_33">33</a>, <a href="#Page_82">82</a>, <a href="#Page_101">101</a><br /> -Henry, A., <a href="#Page_126">126</a><br /> -Hirase, Prof., <a href="#Page_124">124</a>, <a href="#Page_125">125</a><br /> -Hofmeister, W. F. B., <a href="#Page_125">125</a><br /> -Hollick, A., <a href="#Page_119">119</a><br /> -Holmes, T. Rice, <a href="#Page_2">2</a><br /> -Hooker, Sir J. D., <a href="#Page_4">4</a>, <a href="#Page_15">15</a>, <a href="#Page_16">16</a>, <a href="#Page_22">22</a>, <a href="#Page_23">23</a>, <a href="#Page_27">27</a>, <a href="#Page_40">40</a><br /> -Hose, C, <a href="#Page_87">87</a><br /> -Huxley, T. H., <a href="#Page_11">11</a>, <a href="#Page_52">52</a><br /> -<br /> -Ireland, Mediterranean plants in, <a href="#Page_30">30-38</a><br /> -<br /> -Jeffrey, Prof. E. C, <a href="#Page_114">114</a>, <a href="#Page_119">119</a><br /> -Jet, <a href="#Page_114">114</a><br /> -Juan Fernandez, <a href="#Page_84">84</a><br /> -Jurassic flora, <a href="#Page_53">53</a>, <a href="#Page_54">54</a>, <a href="#Page_70">70</a>, <a href="#Page_117">117</a><br /> -Jussieu, A. de, <a href="#Page_109">109</a><br /> -<span class="pagenum"><a name="Page_141" id="Page_141"> 141 </a></span><br /> -Kaempfer, E., <a href="#Page_121">121</a><br /> -Kauri Pine, <a href="#Page_107">107</a><br /> -Kidston, Dr E., <a href="#Page_74">74</a>, <a href="#Page_80">80</a><br /> -Knaresborough, petrifying spring at, <a href="#Page_64">64</a><br /> -Krakatau, new flora of, <a href="#Page_33">33</a>, <a href="#Page_31">31</a><br /> -<br /> -Laccopteris, <a href="#Page_90">90</a>, <a href="#Page_91">91</a><br /> -Lang, Dr A. , <a href="#Page_27">27</a><br /> -Lankester, Sir Edwin Ray, <a href="#Page_49">49</a><br /> -Lhwyd, E., <a href="#Page_57">57</a><br /> -Linnaeus, C, <a href="#Page_121">121</a>, <a href="#Page_123">123</a><br /> -Liriodendron, <a href="#Page_28">28</a>, <a href="#Page_29">29</a><br /> -Liverworts, antiquity of, <a href="#Page_79">79</a><br /> -London Pride, <a href="#Page_31">31</a><br /> -Longevity of trees, <a href="#Page_1">1-10</a><br /> -<i>Luzula racemosa</i>, <a href="#Page_23">23</a><br /> -<i>L. spicata</i>, <a href="#Page_23">23</a>, <a href="#Page_24">24</a><br /> -<br /> -MacDougal, Prof., <a href="#Page_62">62</a><br /> -Maiden Hair Tree, <a href="#Page_120">120-133</a><br /> -Mammoth trees of California, <a href="#Page_95">95-105</a><br /> -Man, first appearance of, <a href="#Page_49">49</a><br /> -Marchantia, <a href="#Page_79">79</a><br /> -Market Harborough, Elodea discovered near, <a href="#Page_20">20</a><br /> -Marshall, E. S., <a href="#Page_38">38</a><br /> -Matonia, <a href="#Page_77">77</a>, <a href="#Page_86">86-94</a><br /> -<i>M. pectinata</i>, <a href="#Page_86">86-88</a>, <a href="#Page_92">92</a>, <a href="#Page_93">93</a><br /> -<i>M. sarmentosa</i>, <a href="#Page_87">87</a><br /> -Matonidium, <a href="#Page_89">89</a><br /> -Mediterranean plants in Ireland, <a href="#Page_30">30-38</a><br /> -Miller, Hugh, <a href="#Page_59">59</a>, <a href="#Page_115">115</a>, <a href="#Page_117">117</a><br /> -Milligan, Dr, <a href="#Page_2">2</a><br /> -Moss, Dr C. E., <a href="#Page_23">23</a><br /> -Mull, Fossil plants in Isle of, <a href="#Page_132">132</a><br /> -<br /> -<i>Naias graminea</i>, <a href="#Page_21">21</a><br /> -Nathorst, A. G., <a href="#Page_64">64</a>, <a href="#Page_103">103</a>, <a href="#Page_117">117</a><br /> -Native plants, <a href="#Page_20">20</a><br /> -New forest, <a href="#Page_31">31</a><br /> -<i>Nipa fruticans</i>, <a href="#Page_50">50-52</a><br /> -Nipadites, <a href="#Page_50">50</a>, <a href="#Page_52">52</a><br /> -Norfolk Island Pine, see <a href="#A_excelsa"><i>Araucaria excelsa</i></a><br /> -<br /> -Oaks, longevity of, <a href="#Page_4">4</a><br /> -Oliver, Prof. F. W., <a href="#Page_74">74</a><br /> -<i>Osmunda regalis</i>, <a href="#Page_76">76-79</a>, <a href="#Page_83">83</a><br /> -<i>Osmundites Dunlopi</i>, <a href="#Page_80">80</a><br /> -<br /> -Palaeozoic plants, <a href="#Page_55">55</a>, <a href="#Page_66">66-68</a>, <a href="#Page_71">71</a>, <a href="#Page_127">127</a>, <a href="#Page_128">128</a><br /> -Peat, trees in, <a href="#Page_12">12</a>, <a href="#Page_13">13</a><br /> -Permian floras, <a href="#Page_55">55</a><br /> -Petrifaction, <a href="#Page_64">64-67</a><br /> -<i>Picea excelsa</i>, <a href="#Page_46">46</a>, <a href="#Page_48">48</a><br /> -Pines, Tertiary, <a href="#Page_65">65</a>, <a href="#Page_66">66</a><br /> -<a id="Pinus_sylvestris"></a><i>Pinus sylvestris</i>, <a href="#Page_11">11-13</a>, <a href="#Page_47">47</a><br /> -Pipewort, <a href="#Page_36">36-38</a><br /> -Pliny's Natural History, <a href="#Page_4">4</a><br /> -Podocarpus, <a href="#Page_109">109</a><br /> -<i>Potamogeton pennsylvanicus</i>, <a href="#Page_21">21</a><br /> -Praeger, E. L., <a href="#Page_32">32</a>, <a href="#Page_36">36</a>, <a href="#Page_37">37</a><br /> -Pre-Glacial plants, <a href="#Page_22">22</a>, <a href="#Page_45">45-48</a><br /> -<i>Primula elatior</i>, <a href="#Page_24">24</a><br /> -Protodammara, <a href="#Page_119">119</a><br /> -Psygmophyllum, <a href="#Page_127">127</a><br /> -<i>Pteridium aquilinum</i>, <a href="#Page_75">75</a>, <a href="#Page_77">77</a>, <a href="#Page_83">83</a>, <a href="#Page_87">87</a><br /> -Pteridophyta, <a href="#Page_18">18</a>, <a href="#Page_124">124</a><br /> -Pteridosperms, <a href="#Page_74">74</a>, <a href="#Page_75">75</a><br /> -Pyrenean plants in Ireland, <a href="#Page_31">31-38</a><br /> -<br /> -Ray, John, <a href="#Page_56">56</a><br /> -Reddish Canal, plants from the, <a href="#Page_21">21</a><br /> -Redwoods of California, <a href="#Page_95">95-105</a><br /> -Reid, Clement, <a href="#Page_13">13</a>, <a href="#Page_22">22</a>, <a href="#Page_45">45</a>, <a href="#Page_102">102</a><br /> -Reid, Mrs, <a href="#Page_22">22</a>, <a href="#Page_102">102</a><br /> -Rhaetic plants, <a href="#Page_54">54</a>, <a href="#Page_94">94</a><br /> -Riccia, <a href="#Page_79">79</a><br /> -<span class="pagenum"><a name="Page_142" id="Page_142"> 142 </a></span>Ridley, H. N., <a href="#Page_25">25</a><br /> -Royal Fern, <a href="#Page_76">76-79</a>, <a href="#Page_83">83</a><br /> -<i>Rubus chamaemorus</i>, <a href="#Page_22">22</a><br /> -<br /> -St Dabeoc's Heath, <a href="#Page_30">30</a>, <a href="#Page_32">32</a>, <a href="#Page_37">37</a><br /> -<i>Salisburia adiantifolia</i>, <a href="#Page_122">122</a><br /> -Saporta, the Marquis of, <a href="#Page_70">70</a><br /> -<i>Saxifraga oppositifolia</i>, <a href="#Page_22">22</a><br /> -<i>S. umbrosa</i>, <a href="#Page_31">31</a><br /> -Scandinavian plants in Britain, <a href="#Page_21">21-23</a>, <a href="#Page_30">30</a><br /> -Scots Pine, see <a href="#Pinus_sylvestris"><i>Pinus sylvestris</i></a><br /> -Scott, Dr D. H., <a href="#Page_74">74</a><br /> -Sequoia, <a href="#Page_5">5</a>, <a href="#Page_95">95-105</a><br /> -<i>Sequoia Couttsiae</i>, <a href="#Page_101">101</a><br /> -<i>S. gigantea</i>, <a href="#Page_5">5</a>, <a href="#Page_95">95</a>, <a href="#Page_96">96</a>, <a href="#Page_98">98-104</a><br /> -<i>S. magnifica</i>, <a href="#Page_104">104</a><br /> -<i>S. novae zeelandicae</i>, <a href="#Page_105">105</a><br /> -<i>S. sempervirens</i>, <a href="#Page_45">45</a>, <a href="#Page_96">96</a>, <a href="#Page_98">98</a>, <a href="#Page_104">104</a><br /> -Sheppey, fossil plants from, <a href="#Page_50">50</a>, <a href="#Page_132">132</a><br /> -<i>Shorea leprosula</i>, <a href="#Page_25">25</a><br /> -<i>Silene acaulis</i>, <a href="#Page_22">22</a><br /> -<i>Sisyrinchium angustifolium</i>, <a href="#Page_38">38</a><br /> -<i>S. californicum</i>, <a href="#Page_38">38</a><br /> -Smith, G., <a href="#Page_75">75</a><br /> -Smith, Sir J. E., <a href="#Page_122">122</a>, <a href="#Page_123">123</a><br /> -Smith, W., <a href="#Page_41">41</a><br /> -Sollas, Prof., <a href="#Page_58">58</a><br /> -<i>Spiranthes romanzoffiana</i>, <a href="#Page_38">38</a><br /> -<i>Stellaria holostea</i>, <a href="#Page_46">46</a>, <a href="#Page_47">47</a><br /> -Steno, <a href="#Page_57">57</a><br /> -Strahan, A., <a href="#Page_13">13</a><br /> -Strawberry tree, <a href="#Page_31">31</a>, <a href="#Page_32">32</a><br /> -<br /> -Tansley, A. G., <a href="#Page_12">12</a>, <a href="#Page_13">13</a>, <a href="#Page_87">87</a><br /> -<i>Taxodium distichum</i>, <a href="#Page_103">103</a><br /> -Tertiary plants, <a href="#Page_31">31-33</a>, <a href="#Page_37">37</a>, <a href="#Page_49">49</a>, <a href="#Page_50">50</a>, <a href="#Page_103">103</a><br /> -<i>Theobroma cacao</i>, <a href="#Page_7">7</a><br /> -<i>Thyrsopteris elegans</i>, <a href="#Page_84">84</a><br /> -<i>Todea barbara</i>, <a href="#Page_11">11</a>, <a href="#Page_78">78</a><br /> -<i>T. radicans</i>, <a href="#Page_78">78</a><br /> -<i>Trapa natans</i>, <a href="#Page_47">47</a>, <a href="#Page_48">48</a><br /> -Triassic period, <a href="#Page_54">54</a>, <a href="#Page_55">55</a><br /> -Tulip tree, <a href="#Page_28">28</a><br /> -<br /> -Walchia, <a href="#Page_113">113</a><br /> -Wallace, Dr A. R., <a href="#Page_85">85</a><br /> -Wealden flora, <a href="#Page_17">17</a>, <a href="#Page_53">53</a><br /> -Weismann, A., <a href="#Page_3">3</a><br /> -Wexford, American plant from, <a href="#Page_38">38</a><br /> -Williamson, Prof. W. C, <a href="#Page_72">72</a><br /> -Wilson, E. 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