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diff --git a/old/62677-8.txt b/old/62677-8.txt deleted file mode 100644 index 15fa12b..0000000 --- a/old/62677-8.txt +++ /dev/null @@ -1,3070 +0,0 @@ -The Project Gutenberg EBook of USDA Bulletin No. 816, by F. L. Mulford - -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: USDA Bulletin No. 816 - Street Trees - -Author: F. L. Mulford - -Release Date: July 16, 2020 [EBook #62677] - -Language: English - -Character set encoding: ISO-8859-1 - -*** START OF THIS PROJECT GUTENBERG EBOOK USDA BULLETIN NO. 816 *** - - - - -Produced by Tom Cosmas - - - - - - - - -Transcriber Note - - Whole and fractional parts are shown as 2-1/2. - Emphasis shown as _Italics_ and =Bold=. - - - - - UNITED STATES DEPARTMENT OF AGRICULTURE - - =BULLETIN No. 816= - - Contribution from the Bureau of Plant Industry - - Wm. A. Taylor, Chief - - - ------------------------------------------------------- - Washington, D. C. [Illustration] January 19, 1920 - ------------------------------------------------------- - - - - =STREET TREES= - - - By - - - =F. L. MULFORD, Horticulturist= - - - Office of Horticultural and - Pomological Investigations - - ------------------------------------------------------- - - - - CONTENTS - - - Page - - Importance of Shade Trees 1 - - Public Control of Street Trees 6 - - Planning for Trees on City Streets 8 - - Spacing Trees 9 - - Conditions for Tree Growth 10 - - Kinds of Trees Suitable for City Streets 14 - Qualities Necessary 14 - Trees for Different Regions 16 - Trees for Special Purposes 20 - - Descriptions of Street Trees 20 - - Culture of Street Trees 43 - Selection of Individual Trees 43 - Preparation of Holes 44 - Planting 45 - Pruning 50 - Stakes and Guards 51 - Later Care 52 - - Care of Mature Trees 53 - Pruning 53 - Feeding 55 - Spraying 55 - - - [Illustration] - - - WASHINGTON - GOVERNMENT PRINTING OFFICE - - 1920 - - -=BUREAU OF PLANT INDUSTRY.= - - William A. Taylor, _Chief_. - K. F. Kellerman, _Associate Chief_. - James E. Jones, _Assistant to Chief_. - J. E. Rockwell, _Officer in Charge of Publications_. - - -Office of Horticultural and Pomological Investigations. - -SCIENTIFIC STAFF. - - L. C. Corbett, _Horticulturist in Charge_. - - -Truck Crop Production Investigations: - - J. H. Beattie. - F. E. Miller. - C. J. Hunn. - B. J. McGervey. - -Irish Potato Production Investigations: - - William Stuart. - C. F. Clark. - W. C. Edmundson. - P. M. Lombard. - J. W. Wellington. - L. L. Corbett. - -Truck Crop Improvement Investigations: - - W. W. Tracy. - D. N. Shoemaker. - -Landscape Gardening and Floriculture Investigations: - - F. L. Mulford. - W. Van Fleet. - -Bulb Culture Investigations: - - David Griffiths. - -Fruit and Vegetable Utilization Investigations: - - J. S. Caldwell. - C. A. Magoon. - C. W. Culpepper. - -Fruit Production Investigations: - - H. P. Gould. - L. B. Scott. - C. F. Kinman. - George M. Darrow. - E. D. Vosbury. - -Grape Production Investigations: - - George C. Husmann. - Charles Dearing. - F. L. Husmann. - Elmer Snyder. - G. L. Yerkes. - -Fruit Breeding and Systematic Investigations in Pomology: - - W. F. Wight. - Magdalene R. Newman. - -Fruit Improvement through Bud Selection: - - A. D. Shamel. - -Nut Investigations: - - C. A. Reed. - E. R. Lake. - -Fruit and Vegetable Storage Physiology: - - L. A. Hawkins. - R. C. Wright. - J. R. Magness. - J. F. Fernald. - -Extension Work (in cooperation with States Relations Service): - - W. R. Beattie. - C. P. Close. - - - - - UNITED STATES DEPARTMENT OF AGRICULTURE - - [Illustration] BULLETIN No. 816 [Illustration] - - Contribution from the Bureau of Plant Industry - - WM. A. TAYLOR, Chief - - Washington, D. C. [Illustration] January 19, 1920 - - - - - =STREET TREES.= - - - By F. L. Mulford, _Horticulturist, Office of Horticultural - and Pomological Investigations_. - - ----- - - CONTENTS - - Page - - Importance of Shade Trees 1 - - Public Control of Street Trees 6 - - Planning for Trees on City Streets 8 - - Spacing Trees 9 - - Conditions for Tree Growth 10 - - Kinds of Trees Suitable for City Streets 14 - - Qualities Necessary 14 - - Trees for Different Regions 16 - - Trees for Special Purposes 20 - - Descriptions of Street Trees 20 - - Culture of Street Trees 43 - - Selection of Individual Trees 43 - - Preparation of Holes 44 - - Planting 45 - - Pruning 50 - - Stakes and Guards 51 - - Later Care 52 - - Care of Mature Trees 53 - - Pruning 53 - - Feeding 55 - - Spraying 55 - - ----- - - - - -IMPORTANCE OF SHADE TREES. - - -The comfort to be derived from shade trees has long been recognized. The -early settlers of this country saved fine trees about their homes, on the -village greens, along the country roads, and in the fields. Later, as -villages grew, the householders planted trees adjoining their properties, -and the result has been the beautiful elm-shaded villages of New England, -the maple-shaded towns of New York and the Ohio Valley, and the oak-shaded -streets of the Southeastern States. (Fig. 1.) - -With time, the villages and towns became cities, and the woodlands were -largely destroyed. Conditions for tree growth were less favorable in the -cities, and nurseries had to be depended upon for planting material. With -these changed conditions the native trees of a region became less dominant -in the city planting and were largely replaced by those trees listed in -nursery catalogues which took the fancy of each property owner along the -street. (Fig. 2.) The quickest growing trees were considered first, and -as some of these made a big showing the first few years and were easily -transplanted, they have become the dominating trees in street planting -from the Atlantic to the Pacific and from the Great Lakes to the Gulf of -Mexico. (Figs. 2, 10, and 13.) A few have planted better and more lasting -trees (figs. 1, 3, and 4); but the tree growth on the streets of the -average town or city is ragged and unkempt in appearance, while that of -the suburb or small village is not much better unless the planting has -been done under municipal control and the plantings on a street have been -confined to a single kind of tree. - -[Illustration: P15311HP - -Fig. 1.--An oak-shaded street in the South. Willow oaks in Birmingham, -Ala., in late summer.] - -[Illustration: P18826HP - -Fig. 2.--A street with mixed plantings. The trees are of different -kinds, some unsuited for the purpose, planted at varying distances -apart, according to the inclination of the property holders. A street in -Stockton, Calif., photographed in early summer.] - -[Illustration: P12515HP - -Fig. 3.--American elms on a city street in midsummer. All these trees were -planted at one time at uniform distances apart by the Commissioners of -Washington, D. C.] - -The advent of such civilizing agencies as the telegraph, the telephone, -the electric light, and the trolley car have added each its share toward -the mutilation or destruction of the good trees that were in existence -at the time of their coming. Faulty methods of pruning also have caused -much disfigurement and ruin. (Figs. 5 and 21.) To this mutilation has been -added the unnecessary destruction of many trees in centers of business -(fig. 6), because they excluded a little daylight, or made a store -less prominent, or were somewhat in the way of using the sidewalk for -merchandise. - -In spite of all these troubles tree planting has continued because people -love trees, enjoy well-shaded streets, and are willing to make efforts to -get them. The trees on well-shaded streets are not only pleasing, but also -contribute toward the health of the community by transpiring moisture into -the atmosphere and by producing a restful effect on eyes and nerves. Red, -especially, is known to have an exciting effect on human beings, and where -city streets are well-shaded it makes less prominent those colors that -might otherwise prevail and offend. - -[Illustration: Fig. 4.--Trees 18 years old on adjacent streets: _A_, Pin -oaks; _B_, ginkgos; _C_, Norway maples. Note the differences in size.] - -Good shade is so appreciated that its presence adds a value to adjoining -properties. Real-estate men recognize this factor and plant shade trees -as early as practicable on land which they develop. That the beauty of a -city is improved by good street trees is becoming recognized more and more -and is finding expression in the desire of garden clubs, civic improvement -associations, and boards of trade for information on this subject. - -Success in planting street trees can be attained only by planning and -controlling the planting as a whole, by selecting the most suitable -varieties, by securing trees in the best condition and planting them -properly, and by giving the necessary later care. - -While towns were small, conditions for tree growth favorable, and -woodlands plenty, so that native trees were easily obtained and started, -the practice of each householder planting his own trees as he saw fit gave -good results. As towns became larger and impervious pavements took the -place of earth roads, the conditions for tree growth became more severe -and the results from the individual planting of trees less uniform. In -large cities the conditions to be met are so extreme that it has become -practically impossible for the average householder to grow street trees -successfully, or to do so only at excessive cost. Then, too, a lineman -in a few minutes often undoes what the individual has achieved with care -and years of patient waiting (see fig. 5). The trees and the lines are -both needed by the public, but when provided by individual initiative -at private expense, but trimmed for the benefit of electric lines by -employees of corporations intent on maintaining service at the least cost, -the trees suffer unduly. - -[Illustration: P16692HP - -Fig. 5.--A tree mutilated by linemen. An otherwise beautiful red oak in -Louisville, Ky., as it appeared in midsummer.] - -In order to have good shade trees at a reasonable cost which receive -timely and efficient attention, with the effective control of wire lines, -the care of the trees needs to be vested in some adequate authority. - - - - -PUBLIC CONTROL OF STREET TREES. - - -Providing shade on city streets is as much a municipal function as -providing lights or sidewalks and should, therefore, be cared for by -public officials. All street trees should be directly under the care of -duly appointed officers, who should be responsible for their planting -and care, as well as for their pruning or removal. Negative control by -requiring permits for planting, pruning, and removal is little better than -no control. - -[Illustration: P16986HP - -Fig. 6.--A desert of asphalt in the business center of a city having less -than 100,000 population.] - -The officials in charge should have the necessary authority and should be -required to initiate and carry forward planting and all other needed work -connected with the establishment and maintenance of street trees. Probably -the most satisfactory way of securing supervision is through an unpaid -commission of three or five members, which in turn employs an executive -officer. In a small place a commission of three persons may be best, one -being appointed every 2 years for a 6-year term. In large places five -members may be better, and the ideal term would be 10 years. A compromise -would be a 5-year term, a new member being appointed each year. The great -need of long-term appointees is that it takes two or three years for a -member of such a board or commission to see and realize the things needed -to be done and the policies that should be carried out. Because it takes a -long time to get results in growing street trees, the policies should be -as nearly continuous as possible and the terms of the members long enough -to insure a majority of experienced persons on the board at all times. - -The method of appointing the commissioners is not so important as that -each shall be selected from the territory as a whole rather than from a -part of it. In some places where the term of service is 10 years, each -one's successor is appointed by the remaining commissioners, subject to -confirmation by the court. Where this is done a member is not permitted to -succeed himself. In other places the commission is appointed by the court; -in others, it is elected by the city legislative body or is appointed by -the mayor subject to the approval of the legislative body. The important -point is to keep the administration as nearly as possible on a purely -business basis. - -A good board can accomplish nothing without liberal funds. There are two -methods of providing these: (1) By an appropriation from the general tax -levy and (2) by direct assessment against the properties, collectible -with the other taxes. If the funds are provided by appropriation, a -fixed minimum, expressed in millage of the tax rate, should be provided -in the organization of the commission. This minimum should be such that -a fair amount of maintenance work can be done when no other funds are -available. Councils that appropriate money sometimes hamper boards by -withholding appropriations. Work of the nature of tree planting should -not be permitted to suffer or be lost by a year's neglect. The fund -provided by this minimum amount should not be so large that regular -additional appropriations will not be needed to carry on the work -properly, as this will give a desirable point of contact of the commission -or board with the ordinary channels of expressing public sentiment in -the district interested. The minimum appropriation mandatory should be -sufficient to prevent injury from lack of care of work already begun. -A period of minimum care and attention while a board and the people or -their representatives are coming to a new understanding of one another's -position is not necessarily a detriment, provided a reasonable maintenance -has been possible in the interim, but without such care the results are -ruinous and work would better not be started than be undertaken with the -possibility of such a period of neglect occurring. - -It is probably desirable to assess the cost of tree planting against -the adjacent property owners at a proportional cost per front foot and -to provide for maintenance out of a general fund. Boulevards and other -unusual developments are sometimes maintained with satisfactory results by -regular assessments against the abutting properties. - -After a proper governing board is provided, the securing of a competent -executive is a matter of ordinary business procedure. It is usually -desirable that he shall be not only a good executive but also a man with -a knowledge of trees and trained in their care, so that he may be a -competent adviser of the board as well as its executive. - -[Illustration: P18857HP - -Fig. 7.--Increased attractiveness due to trees on a city street, as shown -by contrasting the two sides of the thoroughfare. If trees like red oaks, -American elms, or the Eucalyptus in the distance had been used, the effect -on this wide street would have been comparable to figure 3. The trees in -the left foreground are umbrella trees. Merced, Calif.; midsummer.] - - - - -PLANNING FOR TREES ON CITY STREETS. - - -With the help of one who knows trees and the local conditions to be -met, the town should be studied and a suitable kind of tree selected -for each street or for a large portion of a street (figs. 1 and 3), -and as conditions warrant the plan should be carried out as outlined. -Mixed plantings of different sorts of trees (figs. 2 and 7) are not as -pleasing and effective as the use of a single species for considerable -distances. The use of only one or two kinds for a whole town is likely to -be monotonous, and it is also undesirable because the variety most used -may become subject to serious disease or insect attacks. The species and -varieties of trees suitable for city planting are few enough, if all are -used, so an endeavor should be made to include as many different kinds as -practicable, assigning one variety for a long stretch of street unless -there is a marked change in its character, in which case a change of trees -would be warranted. - -Where trees are already on a street, the problem of planning for the -future is frequently much complicated, especially if there are several -kinds in good condition. Where there is but one good kind, gaps can be -replanted with young trees of that sort. If there are poor trees of a good -variety or trees of a poor or short-lived variety it would be advisable -to remove these and do all the replanting at one time, so as to have the -trees on the street as nearly uniform as possible. Where there are several -good varieties in good condition the sensible thing is to care for the -trees that are there and then, after careful study, decide on one variety -for all future plantings on that street. - -[Illustration: P14631HP - -Fig. 8.--Trees 20 feet apart that should be at least 60 feet apart. -Sycamores in Washington, D. C., as they appear in late winter.] - - - - -SPACING TREES. - - -A common fault in all street planting is to put the trees too near -together. (Fig. 8.) This is more evident where the work has been done by -the abutting property owners than by municipalities. - -After trees are started and have attained some size it is extremely -difficult to get them removed, even where the good of the remaining trees -demands it. The removal of a fairly good tree merely because it is short -lived in order to make room for a good one that will be permanent does not -appeal to the average citizen. Where trees which have been planted by the -property holder come under city control a strong feeling of proprietorship -still remains, which is outraged by the suggestion of the removal of even -poor trees. Where all the work is under city control good work is often -hampered by a strong public sentiment against the removal of trees, even -though they are poor or crowding. - -Because of this difficulty it is extremely important that young trees be -planted farther apart than at that time seems reasonable. If they are -planted as far apart as is proper for mature trees the distance will be -so great as to make planting seem a joke. If they are planted half the -distance apart they should be when mature, good results would follow if -the intermediate trees were removed when they nearly touch those to be -left. As the intermediate trees would probably not be removed, or not -until too late for the good of the remaining ones, planting had better -be sufficiently far apart in the beginning to avoid the necessity of -later removals. In the beginning the trees will be too far apart and when -mature too close together, but it seems to be the alternative imposed by a -misguided public opinion. - -There is scarcely a community that would permit the removal of -interplanted trees from a street of fine elms, oaks, or other worthy -varieties without a protest that would be the almost sure political -death of the administrative authorities responsible, no matter how great -the need or how much expert support they might have. If short-lived -intermediate trees were used they would not be likely to be taken out -before they died, and they probably would not die before they had -irreparably injured the permanent trees. The removal of surplus or -interplanted trees can be made with least shock to the community by -gradually narrowing the tree tops by severe pruning from year to year on -the sides next the permanent trees until finally they are so narrow they -may be removed and leave only small openings between the permanent trees. -Even this method will not materially lessen the public protest at the -final removal. - -A common practice is to set street trees 35 feet apart. If it were -practicable to remove one-half the trees at the proper time this would be -a good distance, but in the eastern half of the United States and on the -Pacific slope 50 feet apart is close enough for most varieties, and for -the larger growing trees 60 to 70 feet would be better. - - - - -CONDITIONS FOR TREE GROWTH. - - -In order to grow, trees must have a soil of suitable texture, in proper -mechanical condition, that contains sufficient available mineral elements -and plenty of organic matter, and, last but not least, a constant supply -of moisture and air. In addition to these there must be in active growth -in the soil many forms of organic life that are in various ways preparing -the material in the soil for the use of the larger plants. Not only must -these things be present, but others that are deleterious must be absent, -whether the substance is hurtful in itself or whether it is an excess of -one that is otherwise beneficial. - -Above the soil three things must be present--air, sunlight, and -moisture--and, as in the soil, harmful things must be absent in order to -have success. Among the deleterious substances are sulphur and other fumes -and soot and other products from incomplete combustion. - -[Illustration: P14633HP - -Fig. 9.--The irregularity in the size of the trees shown is due to a -part of the first planting having been killed by illuminating gas from -defective pipes. Norway maples as seen in Washington, D. C., in late -winter.] - -Some of the more obvious things with which a city tree has to contend are: -Water-tight pavements, both on the sidewalk and street, that prevent the -admission of air and water; the removal of the topsoil in street grading, -thus forcing the tree to exist on the good soil provided in the hole; -careless digging near the tree for gas, water, and electric service, and -especially for the placing of curb-stones; the saturation of the soil with -illuminating or sewer gas from defective pipes (fig. 9); the pouring of -salt water from ice-cream freezers into gutters, where it may find its way -into the soil near tree roots; the gnawing of the trunks by horses; and -the cutting of the tops by linemen and tree trimmers. - -Because of the uncongenial conditions for the growth of trees on city -streets comparatively few kinds are satisfactory for such use. Among -those available are some that will grow under extremely trying conditions. -Kinds can be found that will thrive wherever it is suitable for human -beings to live. If it is impossible to grow trees on a street, as a health -measure that street should be closed for human use until conditions are so -improved that it will support trees. - -[Illustration: P15298HP - -Fig. 10.--A business center relieved by a parking with Carolina poplars. -Macon, Ga.; late summer.] - -More kinds will thrive under suburban conditions where only a small -portion of the roadway is covered by an impervious coating, where the -parking spaces are liberal, and where the street is lined with open lawns -than under the conditions in a city, where the street is covered with a -water and air proof coating and the sidewalks with an impervious material, -where parking spaces are limited, and where adjoining lawn areas are small -or lacking. By a careful selection of kinds, all conditions in a city can -be met. In some places bad conditions could have been improved greatly by -a little forethought; in others, such conditions can be bettered. These -details, like many other matters connected with city planning, have been -ignored, but should be considered immediately, especially by villages and -small cities. Figure 6 shows how an opportunity for creating a beauty spot -has been lost sight of, while figure 10 shows how a city has utilized less -ground to increase the comfort and attractiveness of its business center. - -[Illustration: P15278HP - -Fig. 11.--A street well proportioned in width of roadway, sidewalk, and -parkings, with willow oaks on the left, American elms on the right, and -young Carolina poplars near the roadway that should be removed. Columbus, -Ga.; midsummer.] - -[Illustration: P14359HP - -Fig. 12.--A street with too much pavement and too little parking space. -Carolina poplars in Baltimore, Md., in midautumn.] - -A common mistake in ambitious young cities and many old ones is to pave -more of the width of the street for traffic purposes than, is likely ever -to be needed. By reducing the roadway and throwing the remainder into -liberal parking spaces much is added to the attractiveness and comfort -of a city. A contrast in the two methods of treatment is illustrated -in figures 11 and 12. The recommendation that the roadway prepared for -travel be made narrow is not to be interpreted as a reason for lessening -the area dedicated to the public use; in fact, in most cities, especially -in the northeastern quarter of the United States, too little space has -been reserved from houseline to houseline (fig. 13). By reserving more -room between the houses and the street for use as lawns and gardens the -conditions would be made more livable, opportunity would be offered for -widening the public way without prohibitive expense if traffic or business -demanded it, and the growing of street trees would cease to be a serious -problem. - -[Illustration: P16842HP - -Fig. 13.--A street with too little room from houseline to houseline. Note -the more attractive appearance of the side with trees. Norway and silver -maples in Frederick, Md., in midsummer.] - - - - -KINDS OF TREES SUITABLE FOR CITY STREETS. - - -QUALITIES NECESSARY. - -Compared with the whole number of trees used for ornamental planting, the -number of kinds suitable for street planting is very small. For use under -city conditions a tree must be adapted to the climate and to the soil upon -which it is to be grown. It must have healthy foliage that withstands -dust and smoke and a root system not easily affected by unusual soil -conditions, by restricted feeding areas, or by root pruning when street -improvements are made. The top should be in proportion to the width of -the street upon which it is used, and it should be rather high headed or -easily trained to that form and of open growth without being too spreading -or sprawling. - -Of minor consideration is the character of the foliage masses, whether -dark or light, heavy and somber or open and airy, and also whether they -have vivid autumn colorings. Only in the most southern parts of the -country and in western California should evergreen trees be considered -for street planting, and then only the broad-leaved evergreens, such as -magnolias and live oaks. In the North the lack of sunshine during the -short cloudy days of winter makes it desirable to admit all the light -possible. Even in the South the question of sunshine should be considered -when selecting varieties. - -[Illustration: P12536HP - -Fig. 14.--Narrow upright trees (Lombardy poplars) on a Barrow Conditions, -it is better street. Washington, D. C.; midsummer.] - -Narrow streets should be planted with columnar trees (fig. 14) or -sometimes with small trees. Broad streets may be planted with spreading -trees (figs. 3 and 16), or, if provided with a central parking space, with -moderate-sized trees in the center and on the sides, or with trees on the -sides suited to the space and formal trees in the center. (Fig. 15.) - -[Illustration: P18856HP - -Fig. 15.--Formal trees in a central parking, but appropriate trees wanting -on the sides of the street. Canary Island date palms in Merced, Calif.; -midsummer.] - -As a rule, trees native to the locality that have been successfully grown -in other cities should be given the preference. When a choice must be made -between untried native trees and those tested in a city or town under -different soil or climatic to give the native trees the first trial. There -are many native trees that are promising which have not been planted on a -sufficient scale or under sufficiently varied conditions to demonstrate -their real value for street planting over any considerable area. Many of -the trees mentioned in this bulletin may prove valuable far beyond the -areas for which they are suggested. The burr oak, the swamp white oak, the -scarlet oak, the chestnut oak, the white oak, the sour gum, and others may -be found on further trial to be as valuable as those already demonstrated -to be valuable over large areas. Those mentioned have all been tested in a -small way. - -Caution should be used in selecting trees with conspicuous flowers and -those with edible fruits or nuts, as in many parts of the country such -trees are badly mutilated by the public. Even horse-chestnuts, although -the nuts are not edible, are often broken by boys clubbing the trees. -That public opinion can prevent such vandalism is in evidence all along -the Pacific coast and at a few places in the East. Every effort should be -made to create a sentiment that will protect these attractive additions to -street adornment, but where the sentiment does not exist it is better to -avoid the planting of such trees except in a limited way. - -[Illustration: P15394HP - -Fig. 16.--Live oaks, the handsomest southern street tree for broad street: -Biloxi, Miss.; late summer.] - -Besides the native trees there are many introduced trees that have proved -valuable and many more that are worthy of trial.[1] A fair trial of -promising introduced trees should be made, and the native kinds should be -thoroughly tested. - -[1] As examples of this are a number of new elms such as _Ulmus -pumila_ and _Ulmus densa_, besides lindens, poplars, and _Koelreuteria -paniculata_, while _Pistacia chinensis_ is suitable for warm regions. -The Office of Foreign Seed and Plant Introduction of the United States -Department of Agriculture will be glad at any time to suggest new trees -that are promising for any region. - - -TREES FOR DIFFERENT REGIONS. - -To simplify the discussion of kinds of street trees likely to prove -satisfactory, the United States has been arbitrarily divided into the -regions shown in figure 17. An endeavor has been made to make each -division cover an area having similar growing conditions, so that the -trees suggested will be likely to thrive in all its parts. A discussion -of the strong and weak points of the different kinds will be found with -the description of the kinds farther on in this bulletin. - - _Region 1._--Region 1 comprises the mild humid portion of the northern - Pacific coast east to the Cascade Mountains, including the western - third of Washington and Oregon and a portion of northern California. - The trees native to western Europe are adapted to this region, as the - climatic conditions are quite comparable. Most of our American trees - also succeed here. - - Some of the desirable varieties for street planting in region 1 are - the Oregon, Norway, sycamore, and sugar maples; California walnut; - tulip; European linden; basswood; sycamore; London plane; white and - European ashes; English and American elms; English, red, and pin oaks; - ginkgo; and the black locust. - -[Illustration: Fig. 17.--Outline map of the United States, showing the -regions within which essentially similar conditions for tree growth exist.] - - _Region 2._--Region 2 is that portion of California lying between - the Sacramento and San Joaquin Valleys and the Pacific Ocean. Many - varieties of trees will succeed here if given water. Because of the - lack of water, unless specially irrigated the more drought-resistant - species should be used. - - Among the deciduous trees useful for this region are the London plane; - the California and common sycamore; English, Huntingdon, and American - elms; Oregon, Norway, sycamore, and English maples; white, green, and - European ashes; red, English, and pin oaks; European linden; basswood; - California walnut; honey and black locusts; horse-chestnut; Albizzia; - and the Japanese varnish tree, or Sterculia. - - Evergreen trees which will probably be successful in region 2 are the - Eucalyptus[2] in variety, acacias, rubber, magnolia, California live - oak, Victorian and poplar-leaved bottle trees, and in the southern - portions the California pepper, silk oak, and jacaranda. Palms are - much planted, but they do not make good street trees except where a - formal effect instead of shade is desired. - -[2] Some cities have ordinances against the planting of certain trees -because their roots sometimes obstruct sewers. Among these trees are the -Eucalyptus in California and some of the poplars in several of the States. - - - _Region 3._--Region 3 comprises the Sacramento and San Joaquin Valleys. - - The deciduous trees for this region are the California walnut; London - plane; California and common sycamores; Oregon, Norway, and sycamore - maples; white, European, and green ashes; red, English, valley, and - pin oaks; European linden; basswood; English and Huntingdon elms; - honey locust; and horse-chestnut. Chinaberries and Texas umbrellas are - much planted in these valleys, but are not good street trees. Olives - and palms are suitable only for formal effects, while eucalypti are - satisfactory but are liable to make trouble with defective sewers. - Acacias grow especially well in this region except in the extreme - north. - - _Region 4._--Region 4 includes the country from the Sacramento and San - Joaquin Valleys to the crest of the Sierra Nevada Mountains. It varies - in elevation and correspondingly in temperature and the amount of - available moisture. - - Where there is sufficient moisture, the deciduous trees recommended - for region 3, except the valley oak and possibly the California - sycamore, may be used. Where there is less moisture the thornless - honey locust, black locust, green ash, hackberry, poplars, ash-leaved - maple, and the American elm if it can be watered the first few years - may be planted. In the warmer sections the chinaberry and Texas - umbrella may be used. - - _Region 5._--Region 5 comprises the hot semiarid country of southern - California and southwestern Arizona which is dependent on irrigation. - - The best deciduous trees for this region are those suggested for the - drier portions of region 4. With ample irrigation the deciduous trees - recommended for region 3 might grow. - - Among the evergreens the Texas palmetto, Parkinsonia, and the - Washingtonia and some other palms can be used where other trees do - not succeed. The red and desert gums may be used also in the drier - regions. With ample irrigation the evergreens suggested for region 2 - should succeed. - - _Region 6._--Region 6 comprises the intermountain section and extends - from the crest of the Cascade and Sierra Nevada Mountains eastward to - the eastern base of the Rocky Mountains. The region includes great - variations in growing conditions, often in very short distances. As a - whole it is semiarid, and in most places trees can hardly be expected - to thrive without more or less irrigation, although in some of the - mountain valleys and on some of the mountain slopes almost ideal - conditions for tree growth exist. - - In the drier parts of the region only those deciduous trees that are - weeds under more congenial conditions can be grown. Those that can - be planted with the greatest hope of success are the thornless honey - locust, black locust, green ash, hackberry, and where the others do - not succeed, the poplars and ash-leaved maple. If it can be watered - for a few years the American elm usually can be grown, and in the - southern half of the region the Mississippi hackberry will probably - succeed. Near the southern border, on lower elevations, the chinaberry - and Texas umbrella can also be planted. In the locations most favored - naturally or where irrigation is possible, the trees suggested for - region 9 can be used. - - Evergreens that may be used for the drier portions of the southern - part of region 6 are the Parkinsonia and the Texas palmetto. - - Native trees may be found that will prove of greater value for limited - areas than any suggested. Cities and towns contemplating street tree - planting would do well to consult the nearest State agricultural - experiment station or the United States Department of Agriculture if - it is thought possible that something better has been found than the - trees suggested. - - _Region 7._--Region 7 is the northern part of the Great Plains area - from the foot of the Rocky Mountains at about the 5,000-foot contour - line east to the ninety-eighth meridian. It is rather uniform in - general conditions, the character of soil having no wide divergence - and the elevation increasing gradually from south to north and east - to west. The rainfall gradually increases from west to east until at - about the ninety-eighth meridian the conditions are more favorable for - tree growth. - - The trees to be relied on are the thornless honey locust, common - hackberry, black locust, green ash, ash-leaved maple, the poplars, - the Chinese elm, and the American elm if it can be watered the first - few years after transplanting. The mossy-cup oak is another tree - worth testing in a small way, as it is native a little east of the - ninety-eighth meridian. The basswood and Norway maple would probably - succeed if supplied with plenty of water. - - _Region 8._--Region 8 is the southern part of the Great Plains. - - In addition to the deciduous trees recommended for the northern Great - Plains (region 7) the Mississippi hackberry, Texas umbrella, and - chinaberry may be successfully grown. - - Evergreen trees that may be used in region 8 are the Texas palmetto - and Parkinsonia. - - _Region 9._--Region 9 is the upper Mississippi Valley, including - the area from that already considered to Lake Michigan and south to - southern Kansas. It is more favorable to tree growth than regions 6 - and 7. - - Trees which will succeed here are the American elm; red, pin, - mossy-cup, and other native oaks; white ash; sycamore; basswood; and - Norway and sugar maples. - - _Region 10._--Region 10 includes the northeastern part of the country - from eastern Illinois to the Atlantic Ocean, and extends southward - through the Appalachian Mountains. It is most favorable for tree - growth. - - The best trees for street planting in region 10 are the red and pin - oaks, London plane, sycamore, the staminate form of the ginkgo, - basswood, tulip, Norway maple, white ash, thornless honey locust, - American elm, and in the southern portion of the region on light land - the sweet gum. The red and sugar maples are among the best trees for - suburban conditions. The hackberry will grow, but should be discarded - in favor of better varieties. The mossy-cup and chestnut oaks are - worthy of trial on gravelly soils in the suburbs. - - _Region 11._--Region 11 includes the lower Mississippi Valley and the - country east of the southern Appalachian Mountains, extending from the - light lands near the South Atlantic and Gulf coasts to the northern - limits of the distinctively southern flora. - - The typical street trees of this region are the willow oaks (fig. 1) - and water oaks, the former a valuable street tree, the latter good - when young but comparatively short lived, with no advantages over the - willow oak. Other good trees are the red, Spanish, laurel, Darlington, - and pin oaks, tulip, sweet gum, American elm, red and Norway maples, - and the ginkgo. - - _Region 12._--Region 12 is the land near the coast from Wilmington, N. - C., to the Mexican border, exclusive of the southern part of Florida. - - Good deciduous trees for this region are the willow, laurel, - Darlington, and Spanish oaks, tulip, sweet gum, sycamore, London - plane, American elm, and the staminate form of the ginkgo. The honey - locust, red or scarlet maple, Norway maple, and the hackberries are - not so good. - - The live oak is the characteristic tree of region 12 (fig. 16) and is - the pride of the cities that have used it. Even though an evergreen, - it is an excellent street tree, as it is large, spreading, and open. - The palmetto and palms thrive and may be used for producing formal - effects. The evergreen magnolia is a good broad-leaved evergreen. - - _Region 13._--Region 13 consists of the southern part of Florida. The - deciduous trees suitable for this section are the willow, Spanish, and - southern red oaks; American elm; Mississippi hackberry; and in the - southern half of the region the Poinciana. - - Evergreen trees are better suited to region 13 than to, any other - portion of the United States except possibly southern California. - Among the best are the live and laurel oaks, evergreen magnolia, - camphor, rubber, silk oak, or grevillea, and casuarina. Eucalypti are - planted to some extent in Florida, but the climate is such that only - on the drier grounds of the interior are they likely to succeed, and - even there they are not to be compared with other excellent species of - trees that may be cultivated successfully. - - -TREES FOR SPECIAL PURPOSES. - -In the heart of a city, where the greatest difficulty is experienced in -getting trees to grow, the ailanthus will probably thrive when nearly all -other kinds fail. The sycamore and the London plane are also good for such -places. The Carolina poplar will frequently grow under these conditions, -and its use may sometimes be warranted. - -For very narrow streets the Lombardy poplar is the best tree. (Fig. 14.) -Trees suitable for use within the reach of ocean spray or on sandy lands -near the coast are the red oak and the red or scarlet maple south to -Charleston, S. C., while the sweet gum and the live oak are equally good -from Norfolk southward and along the Gulf of Mexico. The red oak, sweet -gum, red maple, and eastern live oak are all grown successfully along -the Pacific Ocean, while the California live oak can be used from San -Francisco southward. The trees that endure the most alkali appear to be -the bladder-nut tree,[3] London plane, peppermint gum,[4] blue gum,[5] -the Washingtonia and other hardy fan palms, Canary Island date palm, the -camphor tree, and _Acacia cyclops_ and _Acacia retinodes_. Only the first -two withstand severe freezing weather. The red oak and the red maple are -worth testing for these conditions. - -[3] _Koelreuteria paniculata_. - -[4] _Eucalyptus amygdalina_ Labill. - -[5] _Eucalyptus amygdalina angustifolia_. - - - - -DESCRIPTIONS OF STREET TREES. - - -ACACIA. - -The acacias, or wattles, are a large group mostly of small trees with -showy yellow flowers. Although much used in California, many of them are -too small to make satisfactory shade trees, and because of shallow rooting -they are injurious to sidewalks. They also stump-sprout badly. They thrive -in regions 2 and 3 and in restricted portions of regions 1 and 5. - -The Australian blackwood,[6] blackwood acacia, or wattle, is a strong, -upright tree, growing to a height of 75 feet and forming a well-shaped -head. It is badly affected by citrus scale, and on this account its -planting is sometimes prohibited. - -[6] _Acacia melanoxylon_ R. Br. - -The black wattle[7] is a strong-growing round-headed tree that reaches a -height of 40 feet and has dark-green leaves. - -[7] _Acacia decurrens mollis_ Lindl. - -The green wattle[8] is a rapid-growing tree, reaching a height of 60 feet -and forming a round head with finely cut leaves. - -[8] _Acacia decurrens_ Willd. - -The silver wattle[9] is much like the black wattle except that its leaves -and young branches are covered with a whitish down. - -[9] _Acacia decurrens dealbata_ F. Muell. - - -AILANTHUS. - -The ailanthus,[10] or tree of heaven, is a tall, broad, handsome tree that -is especially valuable in the heart of closely built or smoky cities. -The staminate and pistillate flowers are borne on separate trees. Only -the pistillate trees should be used, as the odor of the blossoms of the -staminate ones is very objectionable for about 10 days in late spring. -These may be produced by grafting from pistillate trees or by propagating -from suckers or root cuttings from such trees if they have not been -grafted. The ailanthus may not succeed in regions 5 and 13. - -[10] _Ailanthus altissima_ (Mill.) Swingle (_A. glandulosa_ Desf.). - - -ASH. - -There are three kinds of ash trees that are useful for street planting. - -The white ash[11] is a large oval-headed tree, reasonably satisfactory -on rich lands in regions 1, 2, 3, 4, 9, 10, 11, and 12, but it is better -adapted to suburban than urban conditions. - -[11] _Fraxinus americana_ L. - -The green ash[12] is one of the few successful trees in regions 6, 7, and -8 and may succeed in region 5. It grows well throughout the remainder of -the United States, but is of less value than other trees there. It is much -smaller than the white ash, with a broad round top. - -[12] _Fraxinus lanceolata_ Borck. - -The European ash[13] is a large, handsome, round-headed tree suited to -regions 1, 2, 3, and 4. - -[13] _Fraxinus excelsior_ L. - - -CAMPHOR. - -The camphor tree[14] is a large, handsome, oval-headed evergreen that will -succeed in the southern half of region 2, in regions 3, 5, and 13, and in -the warmer parts of region 12. It will endure more frost than the orange, -and where it is successfully grown it is deservedly popular. - -[14] _Cinnamomum camphora_ (L.) Nees and Eberm. - - -CHINABERRY. - -The chinaberry,[15] sometimes known as the China tree, is a small, -round-headed, short-lived tree that will grow in regions 2, 3, 5, 8, 11, -12, and 13 and near the southern edge of region 6. It is too short lived -to be considered for planting where other trees will grow. - -[15] _Melia azedarach_ L . - -The umbrella tree,[16] or Texas umbrella, is a small, compact form of the -chinaberry with an umbrella-shaped top. It is useful for formal effects, -as in the parking on a wide street where taller trees are used on the -side. It will grow in regions 2, 3, 5, 8, 11, 12, and 13 and in the -southern parts of region 6. - -[16] _Melia azedarach umbraculiformis_ Berckmans and Bailey. - - -ELM. - -The elms are large, handsome shade trees suitable for use over a wide -range of territory. - -[Illustration: P12460HP - -Fig. 18.--An American elm with crotches liable to be split by heavy winds. -Note the supporting chains.] - -The American elm[17] sometimes called the white elm and water elm, is -one of the handsomest American shade trees. (Fig. 3.) It has been the -standard street tree of New England, giving to the roadsides and village -streets the characteristic appearance which is so attractive to summer -visitors. - -[17] _Ulmus americana_ - -The American elm is tall and spreading, and where planted as near together -as is customary on streets and country roads the effect of the mature -trees is that of an arch formed by the growing together of their spreading -tops. It is of rapid growth and long lived. - -This elm drops its leaves very early in the fall, but it comes into leaf -early in the spring. Because of its manner of branching it is especially -liable to be split by heavy winds. This trouble may be lessened by -selecting and planting specimens with a close, compact habit of growth or -possibly also by great care in training young trees. Two limbs separating -from one another by a very small angle, that is, when they start to grow -in nearly the same direction, make a crotch that is liable to split. (Fig. -18.) Where two limbs separate at nearly a right angle or where three or -more limbs of about equal size grow from a common point or very nearly so, -the crotch is likely to be much stronger. Careful pruning and training to -provide a proper system of branches may be especially helpful with this -elm. - -Because of the attacks of the elm leaf-beetle[18] and the European elm -bark louse,[19] many handsome trees have been severely damaged or killed -before communities were properly equipped for fighting them, for with -careful spraying these insects may be kept in check. However, on account -of the existence of these pests and because they are gradually spreading -to new territory, tree planters should consider carefully whether it -is advisable to plant the elm in their localities. Where there is no -danger from these insects, this elm is one of the best of street trees. -Consultation with the nearest State agricultural experiment station or -with the Entomologist of the United States Department of Agriculture would -be advisable in order to determine this point. - -[18] _Galcrucella luteola_ Mull. - -[19] _Gossyparia spuria_ Mod. (Data regarding both insects furnished by -the Bureau of Entomology.) - -The best specimens are to be found in the northern part of region 10, -although the elm is being grown all over the United States and is proving -a valuable street tree even in towns and villages of regions where the -rainfall is as low as 15 inches. It is not recommended for planting in -regions 3 and 5. - -The English elm[20] is a tall, oval-headed, compact, handsome tree with -leaves smaller than the American elm and which stay on much later in the -fall. In regions 1 and 2 it is at its best, in the former equaling the -American elm and in the latter excelling it. It also thrives in regions 3 -and 10 and in the eastern part of region 11. - -[20] _Ulmus campestris_ L. - -The Huntingdon elm[21] is a comparatively round-headed European variety. - -[21] _Ulmus hollandica vegeta_ (Lindl.) Rend. - -It is a large, handsome tree with good foliage and is more compact in -growth than the American elm. It succeeds well in regions 1, 2, 3, and 4. - -The wahoo, or winged elm,[22] is native to the South Atlantic and Gulf -States near the ocean. It has larger leaves than the American elm and is -not as spreading in its growth, but it succeeds well on city streets in -regions 11, 12, and 13. - -[22] _Ulmus alata_ Michx. - - -EUCALYPTUS. - -There are a large number of species of Eucalyptus, many of which can be -used for street planting in regions 2, 3, and 5. Some cities prohibit -their planting because their roots are liable to penetrate defective -sewers, and in other cities they must be kept at least 70 feet from a -sewer, though even this distance may not prove permanently effective. - -The roots of any tree are liable to find their way into a defective -sewer, but the trees mentioned are especially noticeable because of their -vigorous root growth. It may be questioned whether a tree should be -condemned for this growth, as it may be better to have a defective sewer -thus revealed than to continue a menace to public health. - -Eucalypti are also being planted in southern Florida, but on account of -the moist climate there it is not to be expected that they will succeed -as well as in the other regions mentioned. They are tall, handsome, -quick-growing trees, usually bearing two kinds of leaves at some time in -their development. - -The blue gum[23] is one of the best eucalypti and the one most commonly -used in California. It is tall, globular headed, handsome, and will -survive several degrees of frost, but it will not withstand the heat of -the deserts in region 5. Its roots are especially liable to invade sewers. - -[23] _Eucalyptus globulus_ Labill. - -The desert gum[24] is one of the trees most resistant to heat and cold, -and it makes a handsome avenue tree. It has pendent branches that have a -tendency to severe splitting with age, but with early attention this may -be overcome largely. It may prove especially valuable for region 5. - -[24] _Eucalyptus rudis_ Endl. - -The manna gum[25] is another Eucalyptus which withstands several degrees -of frost and makes an excellent roadside tree. Some forms shed their bark -in long bands that leave the trunks almost white. Many people consider it -a dirty tree on this account. - -[25] _Eucalyptus viminalis_ Labill. - -The red gum[26] grows with a broad head, is one of the most resistant of -the eucalypti to frost, drought, and heat, and succeeds wherever any of -these trees can be grown in regions 2, 3, or 5, but is most useful in -region 5. - -[26] _Eucalyptus longirostris_ F. Muell. - -The sugar gum[27] is a drought-resistant variety, but it does not -withstand cold. It is a common roadside tree in southern California, but -becomes straggling with age. - -[27] _Eucalyptus corynocalyx_ F. Muell. - - -GINKGO. - -The ginkgo,[28] or maidenhair tree (fig. 4, _B_), is a native of Japan -that thrives in a cool climate or a hot, moist one and succeeds in regions -1, 9, 10, 11, 12, and 13. It is extremely erratic in its behavior, -sometimes growing well, sometimes practically not growing at all, but -where it succeeds it is very disease resistant, and it withstands severe -windstorms remarkably well. The leaf is peculiar in appearance, resembling -in outline a much enlarged leaflet of maidenhair fern with a corrugated -surface. The tree is conical when young, but as it reaches maturity its -top usually fills out, making a broad, almost flat-topped, handsome tree. -Only the staminate form should be used, because the pistillate form bears -fruits the flesh of which is slippery and dangerous when it drops to the -pavement, and to some people it is somewhat poisonous to the touch. Ginkgo -trees, therefore, would need to be secured by budding or grafting from the -mature staminate form. - -[28] _Ginkgo biloba_ L. - - -HACKBERRIES. - -The hackberry,[29] or sugarberry, is especially valuable in regions 6, 7, -8, and 9, as it grows satisfactorily where there is comparatively slight -rainfall. It is also much used in region 11, but should be superseded -there by other varieties that are better. It is of moderate size with an -oblong head and of rather open growth. It is comparatively short lived. -Its leaves are much like those of the elm. - -[29] _Celtis occidentalis_ L. - -The name sugarberry comes from the sweet black berries that are borne -in the early fall. The tree is sometimes affected by a fungous trouble -known as witches'-broom. This trouble causes large numbers of small -sprouts to start from the affected portion, which gives the infected tree -an unsightly appearance. The hackberry should not be planted where this -trouble is prevalent. - -The Mississippi hackberry[30] is a large, open, oblong-headed tree with -smoother leaves than the common hackberry. It is useful in the southern -part of region 6, in region 8, and to some extent in regions 11 and -12. It thrives well under the same adverse moisture conditions as the -common hackberry. The trunk and the large branches have little wartlike -projections of the bark scattered irregularly over them. The small twigs -are sometimes more or less spotted or winged in the same way. The tree is -rather larger than the common hackberry and apparently is less subject to -witches'-broom. - -[30] _Celtis mississippiensis_ Bosc. - - -HONEY LOCUST. - -The honey locust[31] is a large, open, round-headed, fine-foliaged tree, -admitting much light through its top. (Fig. 19.) The common form has stiff -spines 2 to 6 inches long, or even longer. There is also a form without -spines, which is the one that should be used for street planting. It is a -useful tree in regions 1, 2, 3, 9, 10, and 11, but is especially valuable -for planting in regions 6, 7, and 8, and may prove useful in region 5. - -[31] _Gleditsia triacanthos_ L. - -[Illustration: Fig. 19.--A street shaded with honey locusts, as seen in -late summer. Washington, D. C.] - - -HORSE-CHESTNUT. - -The horse-chestnut[32] has handsome blossoms that are very showy, and -when in bloom an avenue of these trees commands attention. It is a close -relative of the buckeye, or Ohio buckeye, which is also a handsome tree, -though less desirable. It is objectionable because it is likely to be -broken by boys clubbing it for its nuts, which are inedible, or where -its leaves are affected with a midsummer blight which makes it unsightly -during the remainder of the season. It is a medium-sized round-headed -tree that does much better under suburban than under city conditions. It -thrives in regions 1, 2, 3, and 10. - -[32] _Aesculus hippocastanum_ L. - - -LINDEN. - -The basswood,[33] or linden, is a large round-headed tree that is -excellent for roadsides in suburban locations and does well on city -streets if the conditions are not too severe. On account of the dark upper -surface and the lighter under surface of the leaves and the sweet-scented -blossoms in early summer it is much admired. It is not as reliable as -some of the other shade trees, as when young it is sometimes attacked at -the base of the trunk by a fungous growth that kills the tree. When once -established it forms handsome avenues. It is suited to regions 1, 2, 3, 4, -7, 9, 10, and 11. - -[33] _Tilia americana_ L. - -The linden,[34] or European linden, has much smaller leaves than the -American linden, or basswood, with more contrast between their upper and -lower surfaces. It is not much different in size, but is a little more -compact in growth and holds its leaves longer in the fall. It is a useful -tree for street planting in regions 1, 2, 3, 4, 9, 10, and 11. - -[34] _Tilia platyphyllos_ Scop. - - -LOCUST. - -The locust,[35] or black locust, is one of the desirable street trees -in regions 6, 7, 8, and probably in region 5, as it thrives with -comparatively little moisture. It makes a moderate-sized oval head that -bears sweet-scented white flowers in late spring or early summer. Its -greatest drawback is its liability to serious injury and disfigurement -by the locust borer,[36] but with proper care this injury can be -prevented.[37] In some parts of the East it is also subject to a leaf -miner[38] that gives its foliage a burned appearance. In region 3 it holds -its seed pods for several years and thus becomes very unsightly. - -[35] _Robinia pseudacacia_ L. - -[36] _Cylene robiniae_ Forst. (Data furnished by the Bureau of Entomology). - -[37] See U. S. Dept. of Agriculture Bulletin 787, entitled "Protection -from the Locust Borer." - -[38] _Chalepis dorsalis_ Thunb. - - -MAGNOLIA. - -The evergreen magnolia[39] is one of the few good evergreen trees for -street planting, but it is adapted only to regions 1, 2, 3, 11, 12, and -13. There are but few conditions that warrant the planting of a tree -having foliage as thick as this, because of the dense shade, which is -especially undesirable in winter. It grows to be a large oval-headed tree -and bears beautiful large white blossoms in late spring or early summer. - -[39] _Magnolia grandifolia_ L. - - -MAPLE. - -Among the maples are some undesirable trees much used for street planting -and some that are valuable only in restricted areas or under special -conditions. The maples are not as satisfactory for street planting as -usually has been supposed, few of the species being suitable for this -purpose and these only in a limited way. The ash-leaved maple, or box -elder,[40] is native to all of the country east of the Rocky Mountains -except the regions near the South Atlantic and Gulf coasts. It is a small, -quick-growing tree that will thrive almost anywhere, but it reaches -maturity early. Because of its early decay and of its being subject to -destruction by wind, it should not be used for street planting where other -trees succeed. It would be a good tree for interplanting were it safe -to risk taking out some of the trees at the right time. The objection -to using these trees is that they would be so likely to look larger -and better than the permanent trees at the time they should be removed -that public opinion would probably resent their removal. There may be -conditions requiring the use of this tree in regions 6, 7, and 8, but it -should be grown only when the other trees suggested for these regions will -not succeed. - -[40] _Acer negundo_ L. - -The English maple[41] is small, round-headed, with small dark-green -leaves, useful in regions 1, 2, 3, and 4. - -[41] _Acer campestre_ L. - -[Illustration: P20042HP - -Fig. 20.--A Norway maple, as seen in late winter, showing its poor shape -when trimmed to a high head.] - -The Norway maple[42] is round-headed and eventually reaches large size, -but, as compared with most of the other maples, it is slow growing (fig. -4, _C_). The persistence of its tendency to form a low head makes it -difficult to give it a high head of desirable shape (fig. 20). It is -also very thickly branched, and its foliage, being heavy and dark-green, -permits but little light to pass through. On this account it is rather -undesirable for street planting. By severe pruning of the interior of -the head this defect may be somewhat overcome. The tree is practically -disease and insect free, with the exception of a liability to infestation -by a leaf aphis[43] which produces yellow spots on the leaves and causes -them to drop prematurely; also, the honeydew which they produce is so -abundant at times as to cover the leaves and wet the sidewalk beneath the -tree, the leaves under certain weather conditions becoming blackened with -dust accumulating and a fungus growing in the secretion, thereby giving -the tree an unsightly appearance. This aphis, however, is not always -present and does not seriously injure the tree. The Norway maple comes -into leaf later than most of the other maples, but holds its leaves later -in the fall. They usually assume a bright yellow hue before they drop. The -leaves are preceded by an abundance of yellow-green blossoms. On account -of its dense shade and masses of fine fibrous roots it is difficult to -grow grass under this tree. Its good shape and attractive dark-green -foliage make it popular for street planting in spite of its dense, low -head. It will succeed in regions 1, 2, 3, 4, 9, 10, 11, and 12. - -[42] _Acer platanoides_ L. - -[43] _Periphyllus lyropictus_ Kess. (Data furnished by the Bureau of -Entomology.) - -The Oregon maple[44] is the large-leaved maple of the northern Pacific -slope. It forms a large round head, and with its unusually large -dark-green leaves makes a very attractive street tree that succeeds well -in regions 1, 2, 3, and 4. It is valuable and worthy of more extended -cultivation on the Pacific coast. - -[44] _Acer macrophyllum_ Pursh. - -The red maple,[45] scarlet maple, or swamp maple is one of the most widely -distributed of American trees. It is found from Canada to the Gulf of -Mexico and west to the Rocky Mountains. Its leaves are the smallest of any -of the eastern native maples, but it grows large and the trees are usually -of rather upright outline. It is better adapted to suburban conditions -than to city streets and is one of the few trees that succeed well near -the ocean. It has bright-red blossoms before the leaves appear. The young -leaves and fruits are also red. The mature leaves begin to color early, -some branches coloring as early as the middle of July, assuming brilliant -reds and yellows and staying on later than those of the sugar maple. It is -a handsome tree that is not as much used as it deserves to be in regions -1, 9, 10, 11, 12, and 13. - -[45] _Acer rubrum_ L. - -[Illustration: P12542HP - -Fig. 21.--Silver maples severely headed back, an improper way to treat -trees, especially silver maples, except under very unusual conditions. -Washington, D. C.; midsummer.] - -The silver maple,[46] also called the soft maple, white maple, and swamp -maple, is probably more used for street planting through the whole -United States than any other tree, and with one exception it is the -least desirable. It is usually planted because it is a quick-growing -tree, but it is not more rapid in growth than several other much better -trees. There are three serious objections to its use as a street tree. -The first is its brittle wood, which at an early age is easily broken -by ordinary windstorms and causes it when a comparatively young tree to -become unsightly. The second is its shallow rooting, which has a tendency -to destroy pavements and also makes it difficult to grow grass near the -trees. The roots also will grow into sewers. The third is the tendency to -decay; the tips of the limbs frequently die, leaving the whole top of the -tree bare of leaves, and the wood decays quickly, especially if the bark -is broken. For this reason it does not stand pruning as well as most other -street trees, and it probably has been pruned more ruthlessly than any -other tree, unless it is the Carolina poplar. It should never be severely -deheaded or, as it is popularly called, "dehorned" (fig. 21), as the stubs -will practically never heal over, and from these cuts decay will start, -which in a very few years will rot the center of the limbs and trunk and -thus destroy the tree. Although it forms a large round head with an open -top and its foliage is pale green above and almost white beneath, making -a very delightful shade, on account of its weaknesses it should never be -used for street planting where other trees can be made to grow. - -[46] _Acer saccharinum_ L. - -The sugar maple,[47] or hard maple, is especially adapted to gravelly -soils in regions 1, 10, and 11, the northern parts of regions 2 and 3, and -the eastern and southern parts of region 9. It is oval-headed, large, and -handsome, having red blossoms which individually are inconspicuous but -which in mass are showy early in the spring before the leaves appear. The -leaves come early, but in late summer they begin to turn brilliant yellow -and red and drop before most other leaves. The sugar maple does not thrive -under city conditions, but is admirably adapted to suburban conditions. - -[47] _Acer saccharum_ Marsh. - -Although the sycamore maple[48] is similar in appearance to the Norway -maple, it is not a satisfactory street tree in the eastern United States. -It succeeds, however, in regions 1, 2, 3, and 4. - -[48] _Acer pseudoplatanus_ L. - -[Illustration: P15662HP - -Fig. 22.--A sugar maple (on the left) and a white oak (on the right), each -32 years old and nearly the same size.] - - -OAK. - -Of the trees used for street planting the oaks are best. They probably -have not been more widely planted because of the prevalent belief that -they are slow growers and because in the North they are rather difficult -to transplant. Although some of the handsomest species, like the white oak -and live oak, are slow growers, those suitable for street planting are -comparatively rapid-growing. The white oak and sugar maple shown in figure -22 are each 32 years old and although differing in shape are practically -the same size, yet the sugar maple is considered a sufficiently -rapid-growing tree to be planted frequently as a street tree, while -the white oak is seldom so used. The oaks are hardy, most of them are -long lived, and for the most part they are free from disease and insect -attacks. Some of the southern species are subject to attacks of mistletoe. - -The California live oak[49] is an evergreen suitable for use in region 2 -and succeeds adjacent to the ocean. It is also useful in region 3 and in -the western part of region 5. It is easily transplanted if handled young, -and especially so when planted from pots. - -[49] _Quercus agrifolia_ Nee. - -The chestnut oak[50] is a native of gravelly soils on eastern mountains -and is suitable for gravelly soils in suburban locations in regions 9, 10, -and 11. It is a large, handsome tree. - -[50] _Quercus montana_ Willd. (formerly _Q. prinus_). - -The Darlington oak[51] is a form of laurel oak especially desirable for -street planting. It is large, round-headed; the leaves are a trifle -smaller and not quite so nearly evergreen as the laurel oak. It is -found wild about Darlington, S. C., where a good form of the laurel oak -appears to have been introduced as a shade tree in the early part of the -nineteenth century. (Fig. 23.) Its range of usefulness lies in regions 11 -and 12. - -[51] _Quercus laurifolia_ Michx. - -The laurel oak[52] is a large, oval-headed tree that is not as rugged and -irregular as the live oak, but is suitable for street planting in regions -11, 12, and 13. It has large, thick, glossy leaves, and in the warmer -regions it is almost evergreen. It is readily transplanted, but as it is -not so common in the woods as the willow oak and the water oak, it has not -been so much used as a street tree. - -[52] _Quercus laurifolia_ Michx. - -[Illustration: P15461HP - -Fig. 23.--A Darlington oak as seen in late summer, Darlington. S. C.] - -The live oak[53] (fig. 16) is probably the noblest and most majestic of -the oaks of regions 12 and 13. It is evergreen and of slow growth, but -wherever it is found, whether on streets or in public parks, it is the -pride of the people. Although an evergreen it is sufficiently open-headed -to make a good street tree. When it becomes old it is spreading and as -a rule does not form as high a head as the willow oak and the laurel -oak. Compared with other southern oaks it is difficult to transplant. -It is of sufficient merit to be used on broad streets, and especially -on boulevards, where the good of the future as well as the present is -considered. - -[53] _Quercus virginiana_ Mill. - -[Illustration: P14413HP - -Fig. 24.--A street shaded with red oaks, Washington, D. C.; midsummer.] - -The burr oak,[54] or mossy-cup oak, is native in the northeastern United -States and west of the Mississippi River on the hills lying between the -river bottoms and the prairies west to the western parts of the Dakotas -and Nebraska and central Kansas and Texas. It is a large; handsome tree -that should prove satisfactory under suburban conditions in regions 7, 8, -9, 10, and 11 and on fertile well-watered soils. - -[54] _Quercus macrocarpa_ Michx. - -The pin oak,[55] sometimes called the swamp oak, is a tall tree, conical -when young, oval at maturity, with a drooping habit of the lower branches. -The leaves are quite finely divided and are of a bright glossy green. -The tree comes into leaf late in the spring and holds its foliage late -in the fall. One objection to the pin oak for street planting is that on -many specimens the dead leaves hang on through the winter. It is adapted -to narrower streets than the red oak, as its habit of growth is not so -spreading. On account of the tendency of the limbs to droop, particularly -as they get older, it is desirable that a good strong leader should be -developed, so that the lower limbs may be removed from time to time as -conditions require. The pin oak thrives on wet and on heavy clay soils, as -well as on a wide range of other soils. Figure 4 shows pin oaks, Norway -maples, and ginkgos 18 years old on adjacent streets, and illustrates the -rapid growth of this oak. At the time of planting these trees the pin oaks -were thought to have the poorest location. This tree is adapted to regions -1, 2, 3, 4, 9, 10, and 11. - -[55] _Quercus palustris_ L. - -The red oak[56] (fig. 24) is probably the best tree for street planting -in regions 1, 9, 10, and 11 and is satisfactory in regions 6, 7, 8, and -12. It is a large, oval, open-headed tree of rapid growth. Under good -conditions a young red oak will grow 4 feet in a single season. Like the -other oaks it is slow in coming into leaf in the spring, but holds its -foliage late in the fall. The leaves usually turn a brilliant red before -they drop. It is comparatively free from insect and fungous attacks, and -it is one of the few trees really suitable for planting close to the -ocean, as it thrives on sandy lands only a few feet above high tide or -within the reach of ocean spray. - -[56] _Quercus maxima_ (March.) Ashe (formerly _Q. rubra_). - -The scarlet oak[57] is a large, open, round-headed tree. Its leaves are -more deeply divided than those of the red oak. As its name indicates, the -leaves turn a brilliant scarlet in autumn, being even more gorgeous than -the red oak. This tree is adapted for street planting and is especially -desirable for suburban conditions in regions 1, 9, and 10. - -[57] _Quercus coccinea_ Muench. - -The swamp Spanish oak[58] is adapted to regions 11, 12, and 13. It belongs -to the red oak group, but is larger than the other oaks suggested for -street planting. It is well adapted to suburban locations, but apparently -it has not been tested under severe city conditions. - -[58] _Quercus rubra_ L. (formerly _Q. falcata_, and certain forms -separated by some botanists as _Q. pagodaefolia_ Ashe). - -The valley oak[59] is a beautiful tree for regions 2 and 3 and the more -favorable parts of region 5. When transplanted young, especially if taken -from a pot, it is easily established where there is opportunity to water -it for a few years. - -[59] _Quercus lobata_ Nee. - -The water oak[60] is frequently confused with the willow oak and the -laurel oak, as these three oaks are not distinguished from one another -except by close observers of trees. It is probably more used than any -other tree in the cities of region 12 and the adjoining portions of region -11. It is the weed of the southern oaks and one of the weeds of the street -trees of the Southern States. It is comparatively short lived and seems -to be more subject to attacks of mistletoe and more easily affected by -windstorms than the willow oak, the Darlington oak, and the laurel oak. -The planting of this tree should be avoided, because it is less desirable -than the other oaks mentioned. - -[60] _Quercus nigra_ L. - -[Illustration: Fig. 25.--Leaves of some of the southern oaks; _A_, Live -oak; _B_, willow oak; _C_, laurel oak; and _D_, water oak.] - -The willow oak[61] (fig. 1), sometimes erroneously called the water oak, -is one of the best of the quick-growing oaks for use in regions 11 and -12. It is frequently used with the water oak for street planting and in -the mind of the average planter is confused with it. It is, however, a -distinct tree, which can be distinguished readily from the water oak. It -is longer lived and is its equal in every other respect. Trees of this -variety which apparently have been planted about 80 years are found in -excellent condition, while water oaks planted at the same time have either -entirely disappeared or are showing marked evidences of decline. Figure -25 shows the characteristic appearance of the leaves of these nearly -related species of oaks. That the willow oak is readily transplanted in -the South when of comparatively large size is proved by the success with -which trees 12 feet high are dug from the woods and planted on the street -(fig. 26). In the extreme South this tree is nearly half evergreen. Its -foliage does not assume the bright colors of the trees of the red oak -class. - -[61] _Quercus phellos_ L. - -[Illustration: P15321HP - -Fig. 26.--Recently transplanted willow oaks, showing trees taken from the -woods as they appeared near the end of the second summer. Montgomery, Ala.] - - -PALM.[62] - -[62] The palms are treated on the basis of notes furnished by Dr. O. F. -Cook, of the Bureau of Plant Industry. - -Several varieties of palms are used more or less for street planting in -regions 2, 3, 5, 12, and 13. Though sometimes effective as a formal street -decoration (fig. 27), they can hardly be considered shade trees. - - -PALMETTO. - -Palmettos, or sabals, abound in region 12 near the coast; succeed -in regions 3, 5, and 13; live in region 2; but are seldom grown -satisfactorily close to the Pacific coast. They can be used effectively -for formal plantings along some streets, park drives, or in liberal -central parking spaces in boulevards, but they are not useful as a -substitute for shade trees. They should have then leaves and damaged roots -cut off in transplanting and should be set about 3 feet deep in their new -location. - -The Carolina palmetto[63] is a native of and useful in regions 12 and 13, -where it sometimes attains a height of 60 or 80 feet. It will thrive in -regions 3 and 5, but is used less there. - -[63] _Inodes palmetto_ (Walt.) Cook. - -The Texas palmetto[64] is especially valuable for southern Texas, where it -is indigenous, and it is likely to succeed generally in regions 3, 5, and -12. It grows to a height of 40 feet and in appearance is quite distinct -from the Carolina palmetto, the leaf segments being much broader and less -drooping.[65] - -[64] _Inodes texana_ Cook. - -[65] The Texas palmetto. _In_ Jour. Heredity, v. 8, no. 3, p. 123, pl. -1917. - -[Illustration: P18989HP - -Fig. 27.--A formal planting on a city street. Palms with interplantings. -Redlands, Calif., in midsummer.] - -The Victoria palmetto[66] is another hardy species, probably a native of -Mexico, but grown for many years at Victoria, Tex. It is similar to the -native Texas species and worthy of general planting in the same region. -A feature of this species is that the persistent leaf bases remain alive -and green for many years instead of turning yellow or brown, as in the -Carolina palmetto. - -[66] Cook, O. F. A new ornamental palmetto in southern Texas. _In_ U. S. -Dept. Agr., Bur. Plant Indus. Cir. 113, p. 11-14. 1913. - - -WASHINGTONIA PALM. - -Washingtonia palms are a very conspicuous feature of street and -ornamental planting in southern California. Two species are represented, -_Washingtonia filifera_ Wendland and _W. robusta_ Wendland. The first is -a native of the canyons and barren slopes that surround the Coachella -Valley of southern California, while the other species probably was -brought by way of the Isthmus of Panama from the region of San Jose del -Cabo, the extremity of Lower California, in the early days of travel. -The name _robusta_ alludes to the fact that this species grows much more -rapidly in height than _W. filifera_, though the trunk is more slender. -Both species are hardy and thrive well through regions 2, 3, and 5, and -also in regions 12 and 13. _Washingtonia robusta_ requires less heat than -_W. filifera_, but both will endure several degrees of frost. Even in -California _Washingtonia robusta_ is distinctly preferable for localities -near the coast. In the vicinity of San Diego the leaves of _Washingtonia -filifera_ become badly infested with a parasitic fungus that does not -attack _Washingtonia robusta_. - - -OTHER HARDY FAN PALMS. - -The species most commonly used for street and ornamental planting in the -California coast districts is the Chinese or windmill palm.[67] This palm -has a slender trunk clothed with brown fibers, flat fan-shaped leaves, -and rather straight radiating segments. The same species is hardy at New -Orleans and Charleston, and even at Laurens, S. C., at an altitude of 600 -feet, but it does not thrive in the sandy soil of Florida. - -[67] _Trachycarpus excelsa_ (Thunb.) Wendl. - -The vegetable hair palm,[68] a native of Spain, Sicily, and North Africa, -is similar to the Chinese palm but smaller and more compact and with -large, sharp spines on the petioles of the leaves. When young it suckers -from the base, like the date palm, so that clusters of it may be formed. - -[68] _Chamaerops humilis_ L. - -The Guadeloupe Island palm[69] is one of the most popular species in -southern California in the region of Santa Barbara, Los Angeles, and San -Diego. This palm is a native of Guadeloupe Island, of! the coast of lower -California, and is not known to occur elsewhere in the wild state. It -is well adapted to the cool coast climate of California, but not to the -interior valleys. It is smaller than the Washingtonia palms, with a rather -short trunk, 15 to 20 feet high, and a dense crown of fresh green leaves. - -[69] _Erythea edulis_ (H. Wendl.) S. Wats. - -The California blue palm,[70] formerly placed in the same genus with -the Guadeloupe Island species, is very distinct in habits as well as -in general appearance, having bluish or grayish green leaves, strongly -toothed petioles, and long, slender inflorescences. The trunk is very -robust, often 2 to 3 feet in diameter, and is said to attain a height -of 30 to 40 feet in Mexico. Several of these features are shared with -the Washingtonia palms. It also has the ability to grow in the dry, hot -interior valleys (regions 3 and 5). In Texas the blue palm has proved -hardy at San Antonio, and even as far north as Austin. - -[70] _Glaucothea armata_ (formerly known as _Erythea armata_). See Cook, -O. F., Glaucothea, a new genus of palms from Lower California. _In_ Jour. -Washington Acad. Sci., v. 5, p. 236-241. 1915. - - -DATE PALM. - -The Canary Island date palm[71] is the most popular palm for park or -street planting, being more hardy than the true date palm, larger and more -vigorous in growth, and producing no suckers from the base of the trunk. -Well-grown specimens in the California coast districts (region 2) with -trunks from 2 to 3 feet thick and immense crowns of spreading deep-green -leaves are among the most imposing forms of plant life. Though less robust -in other regions, the species is very hardy and adapted for planting -anywhere in the palm belt (regions 3, 5, 12, and 13). - -[71] _Phoenix canariensis_ Hort. - -The true date palm[72] is adapted to the warmer parts of regions 3 and 5, -but it is much inferior to the Canary Island species for ornamental use -because the foliage is less attractive, due to its habit of sending out -suckers from the base of the trunk. - -[72] _Phoenix dactylifera_ L. - - -THE COCONUT AND ITS RELATIVES. - -The true coconut palm is confined to a narrow belt along the coast of -southern Florida, but other species of cocos are planted in the coast -districts of California. The species that is most prominent in park and -street plantings around San Diego, Los Angeles, and Santa Barbara is -usually known as _Cocos plumosa_ or _Cocos romanzoffiana_, and is a rather -tall, slender palm with a long-jointed trunk about 1 foot in diameter -and long, spreading, feathery, deep-green leaves. Another series is -represented by _Cocos yatay_ and several similar species, often called -_Cocos australis_ in nursery catalogues. They have short, thick trunks, -very glaucous grayish or bluish foliage, and fleshy edible fruits, highly -flavored, somewhat like pineapples. These gray-leaved species are very -hardy. Another coconut relative is the Chilean molasses palm,[73] which -has a massive trunk 3 or 4 feet in diameter, specimens of which are -growing at a few places in California. - -[73] _Jubaea chilensis_ Baill. - - -OTHER PINNATE PALMS. - -The amethyst palm, a native of Australia, is commonly planted in -California. It usually appears in lists and nursery catalogues as -_Seaforthia elegans_ or _Archontophoenix alexandrae_, but it is now -recognized as distinct from both of these species and has received a new -name, _Loroma amethystina_. It is the only pinnate-leaved palm, except -certain species of Phoenix and Cocos, that grows freely in the open air -in the coast districts of California, from Santa Barbara to San Diego. -In habit and general appearance Loroma is more like the royal palm, -though with a smaller trunk and fewer leaves. The pinkish purple drooping -inflorescence is very attractive and develops into a large cluster of -scarlet berries. - - -The royal palms, species of Roystonea, are perhaps the most striking -ornamental members of the whole group. They can be grown in southern -Florida and even exist in the wild state in some of the hammocks below -Miami. - - -PEPPER TREE. - -The California pepper tree[74] is much used in regions 2 and 3 and in the -western part of region 5. It is a moderate-sized broad-headed tree with -fine foliage, which gives it a light, airy appearance. During the fall -and winter it is covered with scarlet berries, which in contrast with the -persistent foliage produce a pleasing effect. - -[74] _Schinus molle_ L. - -[Illustration: Fig. 28.--A pavement heaved by the roots of poplar trees.] - - -POPLAR. - -Poplars are not desirable for street planting. Their wood is brittle and -easily broken by ordinary windstorms, and their roots run near the surface -and are likely to interfere with pavements, as shown in figure 28, while -those of some varieties are especially liable to make trouble in sewers -by filling them with a mass of fibrous roots if access is once gained. -Vigorous root growth is encouraged by the moisture from a leak, and the -roots ultimately find their way inside. - -The southern cottonwood,[75] Carolina poplar, and the northern -cottonwood[76] are so similar in their adaptability for street planting -purposes that they will be discussed together. They are easily propagated, -easily transplanted, are quick-growing, and where they reach maturity -under normal conditions form very large oval-headed handsome trees, but -under the artificial conditions existing in cities it is necessary to -prune them quite severely when young to remove the long vigorous growths -and make the heads more compact. This pruning stimulates more vigorous -growth, which must be removed or they will form long branches with heavy -tops, that are especially liable to be injured by windstorms. The more -they are pruned the greater the tendency to an undesirable form of growth. -They begin dropping their leaves early in the summer and lose them very -early in the autumn. Their root growth is especially vigorous, so that -they are liable to make trouble in sewers in the manner already mentioned. -It is largely on this account that many cities prohibit the planting of -these trees. Except in regions 6, 7, or 8 or in locations where smoke and -fumes in the air prevent the growing of other trees, they should not be -planted. - -[75] _Populus deltoides_ Marsh. - -[76] _Populus virginiana_ Fouger. - -The Lombardy poplar[77] is a tall columnar tree adapted for use on very -narrow streets (fig. 14). It is short lived in many places, due largely to -the European poplar canker, but otherwise is a satisfactory tree for these -conditions in all parts of the United States. The trees may be planted as -close together as 30 feet. - -[77] _Populus italica_ (Du Roi) Moench. - -None of the other poplars have much to recommend them for street planting. - - -RUBBER TREE. - -The rubber tree[78] is a large-headed handsome evergreen, suitable for -regions 3 and 5 and the southern parts of regions 2 and 13 when the use of -an evergreen tree is warranted. - -[78] _Ficus elastica_ Roxb. - - -SILK OAK. - -The silk oak,[79] or Australian fern, is a large, handsome tree that -succeeds well in regions 2, 3, and 13; also in region 5 if provided with a -reasonable amount of moisture, as it stands drought remarkably well. It is -covered in early summer with orange-colored flowers. - -[79] _Grevillea robusta_ A. Cunn. - - -SWEET GUM. - -The sweet gum[80] is adapted to regions 11, 12, and 13, especially on -sandy lands. It forms an oval-headed, handsome tree with star-shaped -leaves that assume a particularly brilliant hue in the autumn. It is -better adapted to suburban conditions than to the heart of a city. Toward -the northern limits of its successful cultivation it is difficult to -transplant, while in the warmer sections of the country it can be moved -with comparative ease. It should be transplanted only in the spring. - -[80] _Liquidambar styraciflua_ L. - - -SYCAMORE. - -The sycamore[81] also called the buttonwood and buttonball tree, is a -large, open, spreading, quick-growing tree native along water-courses. -It is adapted to regions 1, 2, 3, 4, 9, 10, 11, 12, and 13 and is worth -testing in regions 5, 6, 7, and 8. Its habit of shedding its outer bark -in large flakes, leaving the white new bark showing in large patches, -makes it a conspicuous tree wherever grown. The fruits are balls 1 inch -or more in diameter and are sometimes objected to because they make dirt -when falling; also the shed bark is considered objectionable. It is such -a strong-growing handsome tree and succeeds so well under city conditions -that it is being planted more and more frequently. It will stand more -pruning and shaping than any other street tree. Without pruning it is -too large for ordinary streets unless spaced at almost double the usual -planting distance, with the trees staggered along the street instead -of being planted opposite. Its high head and open habit of growth are -distinct advantages for street planting. Its foliage, too, is a light -green, which gives an impression of airiness with the shade. It is subject -to attack by a fungus that kills the leaves while still small or partially -mutilates them, giving them an unsightly appearance. In some places this -trouble is quite serious. - -[81] _Platanus occidentalis_ L. - -The California sycamore[82] is a native of California adapted to regions -1, 2, 3, and 4 and portions of region 5. It is similar in general -characteristics to the sycamore. - -[82] _Platanus racemosa_ Nutt. - -The London plane tree[83] is one of the Old World forms of sycamore. -According to Alfred Render,[84] "the true oriental plane is rare in -cultivation, the tree usually planted under this name being _Platanus -acerifolia_" It it more compact in habit of growth and has the other good -qualities of the sycamore. It is being more and more used on city streets -and is proving satisfactory in regions 1, 2, 3, 4, 9, 10, 11, and 12. It -will probably succeed in the warmer parts of regions 6 and 7 and also in -regions 5 and 8. It is a more desirable tree for ordinary use than the -sycamore, on account of its more compact habit and comparative freedom -from disease, though it is tender in the northernmost sections. - -[83] _Platanus acerifolia_ (Ait.) Willd. - -[84] Bailey, L. H., ed. New York, 1916. Standard Cyclopedia of -Horticulture, v. 5, p. 2707. - - -TULIP TREE. - -The tulip tree[85] is also sometimes called the tulip poplar or yellow -poplar, though the latter names are unfortunate, as the tree is not -a poplar or even closely related to the poplars. It is a large, -rapid-growing tree suitable for suburban conditions in regions 1, 2, 10, -11, and 12. The leaves are of unusual form, the upper half appearing to -have been cut away, leaving a notch about where it would seem the middle -of the leaf should be. The color is a light green. The roots are unusually -soft and tender, and therefore the tree needs to be transplanted quickly -and with great care. Small sizes should be planted, especially near the -northern limits of growth. It should be transplanted only in the spring. -If after transplanting it the top should die and a new vigorous shoot -should put out from the root, it would be desirable to form a new top from -this shoot rather than to transplant another tree. - -[85] _Liriodendron tulipifera_ L. - - - - -CULTURE OF STREET TREES. - - -SELECTION OF INDIVIDUAL TREES. - -Nursery-grown trees should be used for street planting, and they should -have been transplanted at least every two years while in the nursery. -This is to insure a thorough root pruning and the production of numerous -fibrous roots close to the trunk. Trees not frequently transplanted form -a few long roots that are largely cut off when the tree is dug. Trees -growing in the woods form a few very long roots, and when an attempt is -made to dig them only a little of the root next the trunk is obtained, -while most of the roots, including the fibrous ones, are left in the -ground. If woodland trees are wanted for street purposes, most kinds -should be grown for a few years in a nursery in order to form a good root -system before being planted on the streets. - -In addition to a good root system, the tree should have a straight -trunk for the variety, with a good set of branches, called the head, -the bottom branches being from 7 to 9 feet from the ground. Trees which -naturally head low should be started with a higher head than those -varieties that have a tendency to an upright growth. A good head for a -shade tree is a leader or upright branch with three or more side branches -about equally spaced around the tree. The trees should be healthy, free -from scars, and also free from evidences of insects or diseases. In the -presence of insects, trees should be thoroughly fumigated along approved -methods before leaving nurseries, to insure against the introduction and -distribution of pests. Weakened vitality resulting from transplanting and -subsequent neglect will frequently invite attack by bark-boring insects -which seriously damage or kill the trees. Mulching and watering will often -prevent this damage. - -Opinion as to the size to plant differs somewhat, but for average -conditions trees from 10 to 12 feet high and with trunks or stems from 2 -to 2-1/2 inches in diameter[86] are very satisfactory in most varieties -used for street purposes. With such varieties as elms sycamores, and some -southern oaks, somewhat larger trees can be used equally well, while -smaller trees would be better in the regions of limited rainfall both -east and west of the Rocky Mountains and for tulip trees and sweet gums, -especially in the northern portion of their range of usefulness. - -[86] Designated by nurserymen as "caliper." - - -PREPARATION OF HOLES. - -Next to the selection of a proper variety, the preparation of the hole -is the most important detail of street tree planting. Because of the -restricted area available for the spread of the tree roots, and owing to -the artificial conditions imposed by the improvement of city streets, the -soil provided for the feeding ground of the roots of the young tree must -be liberal in quantity and of the best quality. From 2 to 3 cubic yards of -soil should be provided for each tree. It is desirable to have at least 18 -square feet of opening in the sidewalk, especially if it is of concrete or -other impervious material. Trees will grow with smaller sidewalk openings, -but they are not likely to thrive so well, and it is impossible properly -to prepare a hole for planting a tree without disturbing at least this -much surface soil. The proper depth of soil is from 2-1/2 to 3 feet. A -hole 3 feet deep large enough to hold 2 cubic yards of soil has a surface -area of 18 square feet. A hole 6 feet long, 3 feet wide, and 3 feet deep -will hold 2 cubic yards of soil, will have the smallest desirable surface -area, and will be of such dimensions as will best conform to the usual -sidewalk and roadway widths and thus not interfere with traffic. - -The tree hole must be so drained that water will not stand in it. If the -soil is so impervious as to hold water some artificial drainage must be -provided. That portion of the depth of a hole that acts as a cistern for -holding water is valueless as a feeding ground for roots. For every cubic -foot of soil in the bottom of a hole that might thus be made valueless by -standing water, 1-1/2 cubic feet of soil should be added by increasing the -length or width of it. Under no circumstances, however, should the depth -of available feeding ground be less than 2 feet. The deeper the roots may -be encouraged to grow, the less injury is likely to be experienced from -drought. - -The soil used should be topsoil from land that has been producing good -crops. This should be well enriched with rotted manure, one part of manure -to four of soil. The addition of such fertilizers as ground bone, tankage, -fish scrap, or cottonseed meal at the rate of 1 pound to the cubic yard of -soil is also helpful. Commercial fertilizers containing mostly phosphoric -acid obtained from other substances than ground bone are not to be -recommended for use in the soil about the roots at planting time. When -used they should form a surface application, worked into the soil after -planting. - - -PLANTING. - -If trees are shipped from a distance they should be taken at once on -arrival to some point where the roots may be carefully covered with soil; -there they should be unpacked and plenty of loose moist earth worked -thoroughly around and over the roots as fast as they are taken from -the box. This temporary covering of the roots is called "heeling in." -(Fig. 29.) The tops may be either erect or laid almost on the ground in -successive rows, the tops of one row lying over the roots of the previous -rows, the object being to cover the roots thoroughly and keep them moist -until the tree is wanted for permanent setting. Not a moment of exposure -should be permitted between the box and the soil. If the roots appear dry, -they may be dipped for a few minutes before "heeling in" in a tub of water -or in thin mud. - -[Illustration: P20370HP - -Fig. 29.--Trees properly "heeled in."] - -[Illustration: P20000HP - -Fig. 30.--Trees handled in a careless manner. The roots should have been -covered with wet canvas.] - -Trees in large quantities are often packed directly in cars with a small -quantity of straw about the roots. When shipped in this way extra care -(compare figs. 30 and 31) must be exercised in taking the trees to the -point where they are to be heeled in. The wagon in which they are to be -hauled should have a tight box, and wet canvas should be tied tightly over -the load. The last is important, so that there may be no chance for the -roots to dry. - -When taking trees from the ground where they have been heeled in to the -place for planting, great care must also be exercised to see that the -roots are not exposed to sun or wind, but are kept closely covered with -moss, wet burlap, or canvas until planted. Lack of care in this matter -is a greater cause of loss in tree planting than carelessness in any -other particular. One city that has its own nursery and uses largely -trees that are supposed to be difficult to move, but is careful about not -exposing the roots for a moment (fig. 31), has a loss of less than 1 per -cent. If the roots once dry the trees will die, and it takes but a short -exposure to dry the roots. The holes should be prepared well in advance -of planting, so that no time will be lost when conditions are right for -putting the trees in the ground. - -[Illustration: P20350HP - -Fig. 31.--A load of trees and tree boxes. The roots are packed in wet moss -and a tree is not taken from the wagon until the planter and two shovelers -are at the hole where it is to be planted.] - -In regions 1, 10, 11, 12, and 13 (fig. 17) the best time for planting -deciduous street trees is the month or six weeks just preceding freezing -weather in the fall. The other desirable time for planting is as soon -after freezing weather is over in the spring as the ground is dry enough -for the mechanical operations. This should be as early as possible, as the -more opportunity there is for root growth before warm weather forces the -top into growth, the better the results are likely to be. In regions 6, 8, -and 9, where the ground freezes to a considerable depth, spring planting -is to be preferred to fall planting unless it is possible to drench the -soil thoroughly for a considerable distance around the trees at planting -time and after that to mulch the soil thoroughly and also to protect the -top from the effect of drying winter winds. Where mice abound they may be -harbored in the mulch and may girdle the tree. This may be prevented by -a collar of wire netting about the base of the trunk or by banking the -earth about it. The death of trees at the time of transplanting is due to -the drying out of either roots or tops before opportunity is given them -to become reestablished in their new locations. This drying may be due to -improper exposure at the time of digging or before packing (fig. 30), poor -packing, prolonged delay in delivery, improper handling between unpacking -and planting, or the existence of conditions conducive to excessive drying -out of the plant after setting. - -[Illustration: P14340HP - -Fig. 32.--A city nursery.] - -The atmosphere is continually claiming a tribute of moisture from all -living plants, whether the plant is in leaf and growing or is dormant. -Growing plants, and dormant plants under normal conditions, are able to -replace this moisture by absorption through the roots. In climates where -newly planted trees may obtain sufficient soil water to replace these -losses by drying, fall planting is best. Where the plants are unable to -get sufficient winter moisture, planting would better be done only in the -spring. Where the soil freezes to a depth greater than that to which the -plant roots extend, the supply of water is cut off from the roots and the -tree will be killed by drying out through evaporation from the top. Where -winter winds are very drying and the soil moisture is limited, evaporation -from the top is likely to be in excess of that supplied by the roots and -the tree is killed in the same way. - -[Illustration: Fig. 33.--Setting a tree: _A_, Measuring from the curb to -get the tree in line; _B_, filling the hole: _C_, placing the box; _D_, -fastening the box.] - -In regions normally adapted to fall planting, newly set trees may be -killed by a dry autumn followed by a dry winter with, high winds or by a -cold winter with so little snow that the ground freezes below the roots. -On the other hand, trees may often be successfully planted in the fall -where such practice is not usually successful by thoroughly mulching the -soil if freezing is the sole cause of the difficulty, or by drenching the -soil thoroughly and then mulching well if lack of moisture and high winds -are the causes of the trouble. Protection from the wind by wrapping the -trunk and large limbs with burlap or some other protecting material is -also desirable. - -After a liberal opening has been made in the specially prepared soil the -tree should be brought, preferably from the city's own nursery (fig. 32), -but if such a nursery has not been provided, then from among the newly -received trees that have been "heeled in" as already described. - -If the tree has been well handled and the roots carefully protected it is -ready for setting. It is desirable to immerse the roots in a thin mixture -of clay and water just before putting it in the hole if there is suspicion -that the roots have been exposed. This can be done before leaving the -nursery or "heeling in" ground, but the roots must be properly protected. -Any mutilated ends of roots should be removed, the top should be severely -pruned, as described later, and the tree should be placed in the hole in -line with the other trees (fig. 33, _A_) and at such a height that after -the filling is completed it will be about an inch deeper in the ground -than it was before transplanting. The roots should be spread out in as -near their original position as practicable, and soil should be carefully -worked in about them with the fingers, so that each rootlet may come in -contact with soil and not be crowded against other rootlets. When all the -roots have been placed and covered the soil should be thoroughly trampled -or tamped to bring the roots into as close contact as possible with it. -Then more soil should be put in and the ground again tamped. Of course, in -order to get satisfactory results the soil used for planting must not be -too wet or too dry. If the soil is in such a state as to hold together in -soggy masses and not spring apart again when squeezed in the hand, it is -too wet for planting. If the soil is too dry, it will not stay in contact -with the roots during the planting operations. A soil that is too dry may -be well-watered a day or two in advance of the planting, or if excessive -dryness does not make it difficult to handle, the tree may be planted and -then be thoroughly watered. After the watering 3 or 4 inches of loose -soil should be spread over the wet ground in order to prevent undue -evaporation. It should not be trampled or pounded in any way after the -water is applied. If trees planted in moist retentive soils are watered -after planting they should be provided with a mulch of similar earth. East -of the Missouri River trees planted in soil that is in good condition -usually do not need watering at the time of planting. - -Trees planted from pots, cans, or boxes should have the ball of earth -taken from the receptacle handled with care, so as not to break it further -than to loosen some of the roots on the outside of the ball; then the soil -should be as carefully placed about this ball and the loosened roots as -about the roots of trees without balls. Trees planted with balls need no -root pruning and little top pruning. - -[Illustration: P20367HP - -Fig. 34.--A pin oak trimmed for planting. Note the bad stubs (_A, A_) on -the left-hand side of the tree.] - -[Illustration: P20368HP - -Fig. 35.--A sycamore trimmed for planting. Well primed, without bad stubs.] - - -PRUNING. - -At planting time the trees should be so pruned as to remove from one-half -to three-fourths of the leaf buds. The head should be formed in the -nursery, so that at planting time the only problem is how to reduce the -amount of prospective growth the first season without destroying the form -of the head. Specific directions are difficult, because different species -of trees are so different in their character of growth. A species that -is naturally compact in growth (fig. 34) should be pruned by removing -whole branches rather than by having the ends of branches removed. One -that is open and spreading (fig. 35) will probably need the shortening -of the longer limbs as well as the removal of interior branches. The -first pruning should be the removal of such branches as can be spared. -If enough buds can not be removed in this way without leaving the head -too open, then the shortening of the branches must follow. It is usually -necessary to remove three-fourths of the limbs to accomplish this. An -expert can do this pruning or most of it more easily before the tree is -planted than afterwards. Some additional pruning may be necessary after -the tree is set. - -In addition to the pruning of the top the roots may need some cutting. -Any broken pieces or ends should be removed, making a clean cut with a -sharp knife, as new rootlets put out more readily from a cleanly cut fresh -surface than from ragged breaks. If the roots are very long, without -branches or rootlets, it sometimes makes planting easier to cut off some -of the ends. As roots are the braces by which a tree is supported in the -ground, it is undesirable to reduce their length unless some positive good -is to be gained by it. - -[Illustration: P20372HP - -Fig. 36.--Types of tree guards.] - -The best implement for cutting small limbs is a sharp knife, and for -larger limbs a fine-toothed saw. Pruning shears are sometimes used, but -they are likely to bruise the wood. If used at all, the blade should -always be turned toward the tree so that the bruise made by the supporting -bar will be on the portion cut off. Where branches are taken off, the cut -should be close to the remaining limb, so that no suggestion of a stub -will remain. (Figs. 34 and 35.) Where ends are cut from branches the cut -should be just above a bud, and the remaining bud should point in the -direction that it is desired the limb should grow. - - -STAKES AND GUARDS. - -Under city conditions young trees need the support of a strong stake as -well as protection for the trunk. Boys like to swing around small trees -or see the tops fly up if bent to the ground. Men find them convenient -hitching posts for their horses, and horses frequently like the taste of -the bark or tear it off for the sake of having something to do. - -Guards are of many forms (fig. 36), from stakes 2-1/2 inches square set 3 -feet in the ground and extending 6 feet above, with heavy-netting placed -about the tree and stapled to the stake, to heavy wooden cribs of four -stakes and intermediate slats and wrought-iron patterns of many forms. - -The trees should be firmly secured to the tops of the guards so that they -will not swing against them in the wind and be rubbed. This is best done -by securing the tree in place in the guard by two loops of pieces of old -garden hose, soft leather, or rope, in such a way as not to bind the tree -too tightly while keeping it from swinging much or rubbing. The essentials -are a firm support for the tree while young with reasonable protection of -the trunk from careless depredations until the tree has reached a diameter -of 6 inches or more. - - -LATER CARE. - -If after planting, the season is dry and it becomes necessary to apply -water, the ground should be soaked thoroughly, and as soon as it has dried -sufficiently to work up loosely it should be hoed or raked to make a good -earth mulch. A mulch of strawy manure or litter may be used in place of -the earth mulch if desired. The watering should not require repeating for -a week or more. - -If the weather becomes warm soon after planting and the trees come into -leaf, wither, and droop, further pruning may save them. The reason for the -difficulty is probably that the growth of the top has been greater than -the newly formed roots can support; therefore the additional pruning is -likely to restore the balance between the top growth and root growth. At -least three-fourths of the remaining young wood should be removed. This -may leave the tree looking almost like a bean pole, but if it induces a -vigorous root growth the top can easily be re-formed. - -Young trees should have an annual inspection, and all crossing branches -and any that are not well placed to form a good head should be removed. -Attention should be given also to all forks, and where two branches start -almost parallel to one another or at a small angle, making a fork liable -to split apart as the tree grows, one branch should be removed. Where -three branches start from almost the same point there is little likelihood -of their splitting apart, but with only two growing at a less angle than -30° there is liable to be trouble in the case of most kinds of trees. On -trees on which few but long shoots form, it may be well to remove the ends -of such shoots. As a rule, it is undesirable to use for street planting -trees with this kind of growth. Young trees should be trained into a -desirable shape by the use of a pruning knife each year, so that a saw -will not be necessary later. Some trees have a tendency to form too dense -a head. The interior branches of these should be removed and the head made -as open as possible while the work can be done with a knife. No attempt -should be made to alter the natural form of a tree but only to insure its -best development. A skillfully pruned young tree will show no evidences of -the pruning after three or four years. - - - - -CARE OF MATURE TREES. - - -PRUNING. - -It is very little trouble to train a tree into a good shape by using the -pruning knife while the limbs are small, but it is usually difficult -to re-form a tree after it has grown to maturity. One who understands -tree growth, however, can often reshape the top of a neglected tree to -advantage, though many who make a business of tree trimming know so little -about it that they do more harm than good. More mature trees have been -hurt by severe pruning than have been helped. Of course, dead or dying -wood should be removed whenever it is found, no matter what the age of -the tree. This should be done by cutting off the limb back to the nearest -healthy crotch. A limb should not be cut off square across (fig. 21) -unless the tree is apparently in a dying condition and the whole top is -treated thus in an attempt to save its life. In such a case, a second -pruning should follow within two years, at which time the stubs left at -the first trimming should be cut off in a proper manner near the newly -started limbs. Healthy silver maples and willows are frequently cut in -this way, but the maples in particular would better be cut down at once -than to subject the public to the dangers of the insidious decay that -almost always follows such an operation on these trees and completes their -destruction promptly. - -Trees that have been neglected a long time frequently have interfering -or crossing branches, or are too low headed or too densely headed for -the place where they are growing. Defects of this kind may be at least -partially remedied. The removal of limbs by cutting them off at a crotch -in such a manner that the wound is parallel with the remaining branch -(fig. 37) inflicts the least possible damage. Such a wound in a healthy -tree will soon heal over if the cut is made through the slight collar or -ring that is nearly always present at the base of a branch. The closer -this cut can be made to the trunk the better the appearance when the cut -is healed. The closer the cut the larger the wound, but the difference -is unimportant if the wood is well protected until it is healed. These -operations are entirely different in purpose and result from the "heading -in" or "heading back" so often practiced under the guise of tree pruning, -either from a false notion of forming a top or for the passage of wires. - -Changing the form of a tree by pruning should not be attempted. Each -species has its own form or forms, and no attempt should be made to -change or distort a tree from its normal habit of growth. Successful -pruning will accentuate rather than disguise a tree's characteristics. - -[Illustration: P20371HP - -Fig. 37.--Part of a tree trunk showing proper and improper methods of -removing old limbs. Although healing has started on the stub (at the -right) it is likely to proceed very slowly. The nearer the cut is to the -tree the larger the wound but the less conspicuous the stub will be when -healed.] - -All cuts should be made so that no stubs or protuberances are left to -prevent quick healing. Small wounds need no after treatment if the cut -is well made. Large wounds should have the wood of the center of the -cut well protected to prevent decay until the new growth has had an -opportunity to heal over the cut. An application made to the center of the -cut to preserve the wood should not be permitted to come near the cambium -layer or inner bark, especially of soft-wooded trees like the tulip and -magnolia, as the oil or other substances contained in the paint, tar, or -other covering may spread to the cambium layer and kill it. It is well not -to make any application within half an inch of the outside of the wound -unless the coating has been thoroughly tested. - -Dead wood should be entirely removed, the cut being made through good live -tissue. Removing such wood frequently exposes decayed cavities, usually -from bad stubs or injuries which have started decay that has followed back -to the main limbs or the trunk. The treatment of such cavities is the -province of tree surgery and is discussed in another publication.[87] - -[87] Collins, J. F. Practical tree surgery. _In_ U. S. Dept. Agr. -Yearbook, 1913, pp. 163-190, pl. 16-22. Published as Yearbook Separate -622, obtainable from the Superintendent of Documents for 10 cents in coin. - -One source of trouble with a large tree that has developed with two trunks -or branches instead of three or more is the liability of their splitting -apart in the crotch. This is especially characteristic of the elm. Careful -attention to the early pruning of trees may eliminate this defect, but -when it exists in mature trees it is frequently advisable to connect the -branches by a strong chain (fig. 18) in order to prevent the limbs from -being torn apart. - - -FEEDING. - -It is difficult to do anything to stimulate the growth of street trees -after they are once started, because usually the only uncovered area over -the roots is the small opening immediately about the tree; hence, the -importance of supplying the best of soil well enriched at the time of -planting. Sometimes a stimulation is desirable, which can be accomplished -by dissolving one-half to 1 pound of nitrate of soda in 50 gallons of -water and applying from 1 to 25 gallons of the liquid, depending on the -size of the tree. Unless the soil is damp at the time of application water -will be needed immediately afterward. This material should be applied only -when the tree is in full leaf and growing. If applied when the tree is -dormant it is likely to be leached from the soil before it is absorbed. -If applied late in the season, that is, within three months of freezing -weather, it would likely stimulate a late growth that would be liable -to be killed the following winter and might make the whole tree more -susceptible to injury from cold. - -Water is one of the great needs of city trees, as the ground surface is -often almost completely roofed over with water-tight coverings. It is -usually a help for the pavement washings to drain into the parking space -where the tree is planted. If a curb is placed about the parking space, -frequent, regular watering is necessary where the ground is thoroughly -covered with water-tight pavements. - -Where growing under suburban conditions, that is, with streets partially -pervious to water, liberal parking spaces, and adjoining lawns, street -trees will respond to all extra care given the near-by open spaces, -whether parkings, lawns, or gardens. If these are well cared for the trees -should have ample sustenance from them without any direct applications. - -In order to prevent the soil about a tree from being packed too hard by -trampling it is frequently desirable on business streets to cover the soil -about it with an iron grating. - - -SPRAYING. - -Street trees, like all other forms of vegetation, are subject to attacks -of insects and diseases. Because of the unfavorable conditions under which -they grow, spraying for biting and sucking insects and suitable treatment -for borers or other burrowing insects require especially careful attention. - -In addition to a number of troubles common to street trees in general, -each species is liable to troubles of its own; hence, the need of -competent supervision by a trained man with an efficient outfit rather -than leaving; the work to individual initiative. - -Because of the height which many street trees attain a powerful outfit is -required to spray them properly. One capable of maintaining a pressure -of 200 pounds per square inch is desirable. The type of spray required -for tall trees is different from that used on fruit trees and other -low plants. For low trees the ideal spray is a mist within a few feet -of the nozzle, application being accomplished by having the nozzles -near the foliage to be treated. For tall trees it is desirable that the -liquid should leave the nozzle in a solid stream, which is broken into -spray as it passes through the air. The material has to be projected -with sufficient force to reach the highest trees before being entirely -converted into mist, as it is impracticable to extend the nozzles into -the trees to reach the farthest portions, as is done with fruit and other -low trees. The spray can not be applied as uniformly as a mist, but it -is impracticable to climb into the tops of shade trees to cover every -part with a cloudlike spray. On the other hand, the mist spray is better -for small trees, as much injury may be done to low trees or to the lower -branches of high trees by the force of the stream from high-pressure -outfits. - -It is estimated that in practice up to 95 per cent of the attacking -insects can be killed with insecticides carefully applied by the stream -method under high pressure. - -In addition to the mechanical problem of satisfactorily covering high -trees with insecticides or fungicides there is the problem of selecting -materials that will be effective against the insects and diseases and -at the same time will not disfigure the paint or stone work of adjacent -buildings with which the materials must inevitably come in contact in -street tree spraying. It frequently happens that the most effective -remedies must be rejected because of the damage they would do to buildings -and that less efficient materials must be used. - -Whitewashing the trunks of trees is a useless and unsightly -practice--useless, as it does not prevent the attacks of insects, and -unsightly, because it makes the trunks of the trees obtrusive when they -should be inconspicuous. - -Banding with cotton or proprietary preparations may occasionally be -useful, but because such applications are so seldom helpful and because -some of the preparations result in injury due to constriction of the -trunks, it should not be resorted to except upon special recommendation of -an entomologist familiar with the existing conditions. - -Details as to enemies to be expected, methods of treatment, and materials -to be used may be found in other publications[88] or may be obtained by -correspondence with the nearest State agricultural experiment station or -with the United States Department of Agriculture. - -[88] See list on following pages. - - * * * * * - - PUBLICATIONS OF THE UNITED STATES DEPARTMENT OF AGRICULTURE - RELATING TO DISEASES AND INSECTS AFFECTING SHADE AND ORNAMENTAL TREES. - - =AVAILABLE FOR FREE DISTRIBUTION.= - - Control of Root-Knot. (Farmers' Bulletin 648.) - - The San Jose Scale and Its Control. (Farmers' Bulletin 650.) - - The Bagworm, an Injurious Shade-Tree Insect. (Farmers' Bulletin 701.) - - The Catalpa Sphinx. (Farmers' Bulletin 705.) - - The Leopard Moth: A Dangerous Imported Enemy of Shade Trees. - (Farmers' Bulletin 708.) - - The Oyster-Shell Scale and the Scurfy Scale. (Farmers' Bulletin 723.) - - The White-Pine Blister Rust. (Farmers' Bulletin 742.) - - Carbon Disulphid as an Insecticide. (Farmers' Bulletin 799.) - - The Gipsy Moth and the Brown-Tail Moth and Their Control. (Farmers' - Bulletin 845.) - - Common White Grubs. (Farmers' Bulletin 940.) - - The Blights of Coniferous Nursery Stock. (Department Bulletin 44.) - - Forest Disease Surveys. (Department Bulletin 658.) - - =FOR SALE BY THE SUPERINTENDENT OF DOCUMENTS, - GOVERNMENT PRINTING OFFICE, - WASHINGTON, D. C.= - - The Mistletoe Pest in the Southwest. (Bureau of Plant Industry - Bulletin 166.) Price, 10 cents. - - The Death of Chestnuts and Oaks Due to Armillaria mellea. - (Department Bulletin 89.) Price, 5 cents. - - New Facts Concerning the White-Pine Blister Rust. (Department - Bulletin 116.) Price, 5 cents. - - The Huisache Girdler. (Department Bulletin 184.) Price, 5 cents. - - Report on the Gipsy Moth Work in New England. (Department Bulletin - 204.) Price, 30 cents. - - A Disease of Pines Caused by Cronartium pyriforme. (Department - Bulletin 247.) Price, 5 cents. - - Food Plants of the Gipsy Moth in America. (Department Bulletin 250.) - Price, 10 cents. - - Dispersion of Gipsy Moth Larvæ by the Wind. (Department Bulletin - 273.) Price, 15 cents. - - The Cottonwood Borer. (Department Bulletin 424.) Price, 5 cents. - - Solid-Stream Spraying against the Gipsy Moth and the Brown-Tail Moth - in New England. (Department Bulletin 4.80.) Price, 15 cents. - - Protection from the Locust Borer. (Department Bulletin 787.) Price, - 5 cents. - - Principal Insects Liable to be Distributed on Nursery Stock. - (Entomology Bulletin 34, n. s.) Price, 5 cents. - - The Locust Borer. (Entomology Bulletin 58, part 1.) Price, 5 cents. - - Additional Data on the Locust Borer. (Entomology Bulletin 58, part - 3.) Price, 5 cents. - - The San Jose or Chinese Scale. (Entomology Bulletin 62.) Price, 25 - cents. - - Report on Field Work against the Gipsy Moth and the Brown-Tail Moth. - (Entomology Bulletin 87.) Price, 35 cents. - - The Importation into the United States of the Parasites of the Gipsy - Moth and the Brown-Tail Moth. (Entomology Bulletin 91.) Price, 65 - cents. - - The Dispersion of the Gipsy Moth. (Entomology Bulletin 119.) Price, - 20 cents. - - The Green-Striped Maple Worm. (Entomology Circular 110.) Price, 5 - cents. - - The Oak Pruner. (Entomology Circular 130.) Price, 5 cents. - - The Dying Hickory Trees: Cause and Remedy. (Entomology Circular - 144.) Price, 5 cents. - - Flour Paste as a Control for Red Spiders and as a Spreader for - Contact Insecticides. (Entomology Circular 166.) Price, 5 cents. - - Three Undescribed Heart-Rots of Hardwood Trees, Especially of Oak. - (Journal of Agricultural Research, vol. 1, No. 2.) Price, 25 - cents. - - A Serious Disease in Forest Nurseries Caused by Peridermium - filamentosum. (Journal of Agricultural Research, vol. v, No. 17.) - Price, 10 cents. - - The Chestnut Bark Disease. (Separate 598, from Yearbook of the - Department of Agriculture for 1918.) Price, 10 cents. - - Practical Tree Surgery. (Separate 622, from Yearbook of the - Department of Agriculture for 1913.) Price, 10 cents. - - Forest Tree Diseases Common in California and Nevada. (Forest - Service Unnumbered Publication.) Price, 25 cents. - - - ADDITIONAL COPIES - - OF THIS PUBLICATION MAY BE PROCURED FROM - - THE SUPERINTENDENT OF DOCUMENTS - - GOVERNMENT PRINTING OFFICE - - WASHINGTON, D. 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