OAK.

[40]Acer negundoL.

The English maple[41]is small, round-headed, with small dark-green leaves, useful in regions 1, 2, 3, and 4.

[41]Acer campestreL.

P20042HPFig. 20.—A Norway maple, as seen in late winter, showing its poor shape when trimmed to a high head.

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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 somewhatovercome. 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 platanoidesL.

[43]Periphyllus lyropictusKess. (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 macrophyllumPursh.

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 rubrumL.

P12542HPFig. 21.—Silver maples severely headed back, an improper way to treat trees, especially silver maples, except under very unusual conditions. Washington, D. C.; midsummer.

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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 earlyage 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 saccharinumL.

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 saccharumMarsh.

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 pseudoplatanusL.

P15662HPFig. 22.—A sugar maple (on the left) and a white oak (on the right), each 32 years old and nearly the same size.

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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.

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 agrifoliaNee.

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 montanaWilld. (formerlyQ. 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 triflesmaller 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 laurifoliaMichx.

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 laurifoliaMichx.

P15461HPFig. 23.—A Darlington oak as seen in late summer, Darlington. S. C.

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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.

[53]Quercus virginianaMill.

P14413HPFig. 24.—A street shaded with red oaks, Washington, D. C.; midsummer.

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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.

[54]Quercus macrocarpaMichx.

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 4shows 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 palustrisL.

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 (formerlyQ. 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 coccineaMuench.

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 rubraL. (formerlyQ. falcata, and certain forms separated by some botanists asQ. pagodaefoliaAshe).

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 lobataNee.

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 nigraL.

Fig. 25.—Leaves of some of the southern oaks;A, Live oak;B, willow oak;C, laurel oak; andD, 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 showingmarked evidences of decline.Figure 25shows 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 phellosL.

P15321HPFig. 26.—Recently transplanted willow oaks, showing trees taken from the woods as they appeared near the end of the second summer. Montgomery, Ala.

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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.

[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.

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 texanaCook.

[65]The Texas palmetto.InJour. Heredity, v. 8, no. 3, p. 123, pl. 1917.

P18989HPFig. 27.—A formal planting on a city street. Palms with interplantings. Redlands, Calif., in midsummer.

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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.

[66]Cook, O. F. A new ornamental palmetto in southern Texas.InU. S. Dept. Agr., Bur. Plant Indus. Cir. 113, p. 11-14. 1913.

Washingtonia palms are a very conspicuous feature of street and ornamental planting in southern California. Two species are represented,Washingtonia filiferaWendland andW. robustaWendland. 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 Panamafrom the region of San Jose del Cabo, the extremity of Lower California, in the early days of travel. The namerobustaalludes to the fact that this species grows much more rapidly in height thanW. 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 robustarequires less heat thanW. filifera, but both will endure several degrees of frost. Even in CaliforniaWashingtonia robustais distinctly preferable for localities near the coast. In the vicinity of San Diego the leaves ofWashingtonia filiferabecome badly infested with a parasitic fungus that does not attackWashingtonia robusta.

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 humilisL.

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 asErythea armata). See Cook, O. F., Glaucothea, a new genus of palms from Lower California.InJour. Washington Acad. Sci., v. 5, p. 236-241. 1915.

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 canariensisHort.

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 dactyliferaL.

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 asCocos plumosaorCocos 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 byCocos yatayand several similar species, often calledCocos australisin 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 chilensisBaill.

The amethyst palm, a native of Australia, is commonly planted in California. It usually appears in lists and nursery catalogues asSeaforthia elegansorArchontophoenix 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.

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 molleL.

Fig. 28.—A pavement heaved by the roots of poplar trees.

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 infigure 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 theyreach 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 deltoidesMarsh.

[76]Populus virginianaFouger.

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.

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 elasticaRoxb.

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 robustaA. Cunn.

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 styracifluaL.

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.

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