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.
The black wattle[7] is a strong-growing round-headed tree that reaches a height of 40 feet and has dark-green leaves.
The green wattle[8] is a rapid-growing tree, reaching a height of 60 feet and forming a round head with finely cut leaves.
The silver wattle[9] is much like the black wattle except that its leaves and young branches are covered with a whitish down.
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.
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.
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.
The European ash[13] is a large, handsome, round-headed tree suited to regions 1, 2, 3, and 4.
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.
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.
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.
ELM.
The elms are large, handsome shade trees suitable for use over a wide range of territory.
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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.
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.
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.
The Huntingdon elm[21] is a comparatively round-headed European variety.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
The English maple[41] is small, round-headed, with small dark-green leaves, useful in regions 1, 2, 3, and 4.
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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.
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.
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.
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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.
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.
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.
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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.
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.
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.
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.
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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.
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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.
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.
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.
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.
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.
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.
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.
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.
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Fig. 26.—Recently transplanted willow oaks, showing trees taken from the woods as they appeared near the end of the second summer. Montgomery, Ala.
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.
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]
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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.
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.
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.
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.
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.
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).
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
