TREES FOR DIFFERENT REGIONS.

P15394HPFig. 16.—Live oaks, the handsomest southern street tree for broad street: Biloxi, Miss.; late summer.

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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 asUlmus pumilaandUlmus densa, besides lindens, poplars, andKoelreuteria paniculata, whilePistacia chinensisis 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.

To simplify the discussion of kinds of street trees likely to prove satisfactory, the United States has been arbitrarily divided into the regions shown infigure 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 discussionof 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.

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.

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.

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 andlaurel 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.

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 andlaurel 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.

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, andAcacia cyclopsandAcacia 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 amygdalinaLabill.

[5]Eucalyptus amygdalina angustifolia.

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 melanoxylonR. 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 mollisLindl.

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 decurrensWilld.

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 dealbataF. Muell.

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. glandulosaDesf.).

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 americanaL.

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 lanceolataBorck.

The European ash[13]is a large, handsome, round-headed tree suited to regions 1, 2, 3, and 4.

[13]Fraxinus excelsiorL.

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.

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 azedarachL .

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 umbraculiformisBerckmans and Bailey.

The elms are large, handsome shade trees suitable for use over a wide range of territory.

P12460HPFig. 18.—An American elm with crotches liable to be split by heavy winds. Note the supporting chains.

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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 hasbeen 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 luteolaMull.

[19]Gossyparia spuriaMod. (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 campestrisL.

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 alataMichx.

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 globulusLabill.

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 rudisEndl.

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 viminalisLabill.

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 longirostrisF. 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 corynocalyxF. Muell.

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 bilobaL.

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 occidentalisL.

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 mississippiensisBosc.

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 triacanthosL.

Fig. 19.—A street shaded with honey locusts, as seen in late summer. Washington, D. C.

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 hippocastanumL.

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 americanaL.

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 platyphyllosScop.

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 pseudacaciaL.

[36]Cylene robiniaeForst. (Data furnished by the Bureau of Entomology).

[37]See U. S. Dept. of Agriculture Bulletin 787, entitled "Protection from the Locust Borer."

[38]Chalepis dorsalisThunb.

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 grandifoliaL.

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 forstreet 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.

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