Populus in the extreme north often forms great forests, and is common on the alluvial bottom-lands of streams and on high mountain slopes, ranging from the Arctic Circle to northern Mexico and Lower California and from the Atlantic to the Pacific in the New World, and to northern Africa, the southern slopes of the Himalayas, central China, and Japan in the Old World. Of the thirty-four species now generally recognized fifteen are found in North America. The wood of many of the American species is employed in large quantities for paper-making, and several species furnish wood used in construction and in the manufacture of small articles of wooden ware. The bark contains tannic acid and is used in tanning leather and occasionally as a tonic, and the fragrant balsam contained in the buds of some species is occasionally used in medicine. The rapidity of their growth, their hardiness and the ease with which they can be propagated by cuttings, make many of the species useful as ornamental trees or in wind-breaks, although planted trees often suffer severely from the attacks of insects boring into the trunks and branches. Of the exotic species, the Abele, or White Poplar, _Populus alba_ L., of Europe and western Asia, and its fastigiate form, and the so-called Lombardy Poplar, a tree of pyramidal habit and a form of the European and Asiatic _Populus nigra_ L., and one of its hybrids, have been largely planted in the United States.
_Populus_, of obscure derivation, is the classical name of the Poplar.
CONSPECTUS OF THE NORTH AMERICAN SPECIES.
Stigmas 2, 2-lobed, their lobes filiform; leaf stalks elongated, laterally compressed; buds slightly resinous. Leaves finely serrate; winter-buds glabrous. 1. P. tremuloides (A, B, F, G). Leaves coarsely serrate; winter-buds tomentose or pubescent. 2. P. grandidentata. Stigmas 2—4, 2-lobed and dilated, their lobes variously divided; buds resinous. Leaf-stalks round. Leaves tomentose below early in the season, broadly ovate, acute or rounded at apex. 3. P. heterophylla (A, C). Leaves glabrous or pilose below. Leaves dark green above, pale, rarely pilose below. Ovary and capsule glabrous. 4. P. tacamahacca (A, B, F). Ovary and capsule tomentose or pubescent. 5. P. trichocarpa (B, F). Leaves light green on both surfaces, glabrous. Leaves lanceolate to ovate-lanceolate. 6. P. angustifolia (F). Leaves rhombic-lanceolate to ovate. 7. P. acuminata (F). Leaf-stalks laterally compressed. Leaves without glands at apex of the petiole, coarsely serrate, thick. Pedicels shorter than the fruit. Disk cup-shaped. Branchlets stout; capsule ⅓′—½′ long. 8. P. Fremontii (G, H). Branchlets slender; capsule not more than ¼′ long. 9. P. arizonica (F, H). Disk minute. Branchlets glabrous; leaves broad-ovate to deltoid, long-pointed and acuminate at apex. 10. P. texana (C). Branchlets pubescent; leaves broad-ovate, abruptly short-pointed or acute at apex. 11. P. McDougallii (G, H). Pedicels 2 or 3 times longer than the fruit; leaves broadly deltoid, abruptly short-pointed. 12. P. Wislizenii (E, F). Leaves furnished with glands at apex of the petiole. Branchlets stout; leaves thick. Winter-buds puberulous; leaves coarsely serrate; branchlets light yellow. 13. P. Sargentii (F). Winter-buds glabrous; leaves less coarsely serrate; branchlets gray or reddish brown. 14. P. balsamifera (A, C). Branchlets slender; leaves thin, ovate, cuneate or rounded at base, finely serrate. 15. P. Palmeri (E).