Spruce.—Perhaps the most important evergreen used in landscape gardening, sharing that position with the pines. They seem to enjoy long winters and short summers, hence are well adapted to the Northern states. As they have a very trim symmetrical shape they can be utilized exceptionally well in formal planting. They go well also with informal planting, lending a splotch of green on an otherwise gray winter landscape. When planted at uniform spacing along an avenue they outline it exceedingly well without very much obstruction to clear vision if they are not set close together. The black (Picea nigra) and white (Picea alba) spruces rise from 40 to 100 feet in height with a compact symmetric conical shape. The black spruce has the darker foliage. The Colorado blue spruce (P. parryana) has been much in vogue as an ornamental tree, the new foliage having a blue tinge. Norway spruce (P. abies) has been used very largely in ornamental cultivation. The cones are large, 5 to 7 inches, nearly cylindrical, and the branches droop in artistic fashion. The Sitka Spruce (P. sichensis) of the Pacific coast region from Alaska to Northern California is a large tree of great commercial importance, and will grow well on low grounds.
Sugar Tree.—See [Maple].
Sycamore.—The plane tree or buttonwood (Platanus occidentalis) is found in the central and eastern portion of the United States, best in the Ohio and Mississippi River basins. It attains a height of 90 to 100 feet, and a spread of half as much. The outer bark peels off, leaving the inner exposed in white patches. Its straight, upright trunk and symmetrical form when allowed free growth ought to commend it for road planting. The fruit are rough balls about an inch in diameter which dangle in the air like ornaments on a Christmas tree. The California sycamore (P. racemosa) is a smaller tree with a poorer quality of wood, but in general appearance somewhat the same.
Tamarack.—See [Larch].
Teak.—A tree of great commercial importance in India and Africa. Has been transplanted to some extent in the Southern states but not yet sufficiently numerous to be considered a road tree.
Thorn.—Several members of the Cratægus family are suitable for landscape planting. Crataegus crus-galli, C. tomentosa, and C. coccinea, native plants, and the English hawthorn, C. oxyacantha, are all recommended where small trees are desired.
Tulip Tree.—See [Poplar].
Tupelo.—Same as Black or Sour [Gum].
Ulmus.—See [Elm].
Walnut.—Three species of walnut are used for road trees—black walnut, butternut, and English (Persian) walnut. The black walnut (Juglans nigra) makes a handsome tree when allowed to develop individually, from 90 to 125 feet high, and 3 to 8 feet in diameter with a normal spread about one-half the height of the tree. The edible nuts are the delight of the small boy and as they are usually gathered up from the ground after they fall their collection will not injure the tree. The foliage is not very dense and it will not take away greatly the fertility of neighboring ground hence, makes an almost ideal road tree. Since the World War, according to Reed[219] it has been considered a favorite as a memorial tree. Its native habitat is the eastern half of the United States intermittently from the Atlantic to Nebraska and Texas, but it thrives when transplanted to the states of Oregon and Washington and is being used extensively by the State of California as a road tree. The trees grow well from the nut or they may be transplanted from a nursery by cutting the tap root one year ahead of transplanting as is necessary for most nut trees. The butternut (J. cinerea), sometimes called white walnut, is a very similar tree, a little smaller and has not quite so extensive a native range. The nuts are not round like the black walnut, but lanceolate in shape. On the whole the black walnut is the better road tree. The English walnut (J. regia) is a native of Persia, but is grown very largely in orchards in California where the annual crop of nuts is more than 20,000,000 pounds. Hardy varieties suitable for more severe climates are advertised but it is not here recommended that they be planted where experience has not shown them to thrive. The tree itself is of fine appearance, and in the warmer climates makes a good road tree.