3 P. tremuloides Mx. American Aspen. Lvs. orbicular-cordate, abruptly acuminate, dentate-serrate, pubescent at the margin; bracts of the ament 3 or 4-cleft, margin silky-fringed. - Abundant in N. Eng. and in the Mid. States, growing in woods and open lands. St. 25 to 40f in height, with a diam. of 8 to 12'. Bark greenish, smooth, except on the trunks of the oldest trees. Lvs. small (2 to 2 1/2' long and of equal or greater width), dark green, petioles 2 to 3' long and laterally compressed, so that they can scarcely remain at rest in any position, and are thrown into excessive agitation by the slightest breeze. The trembling of the "aspen leaf" is proverbial. Aments plumed with silken hairs, about 2' long, pendulous. Apr.
4 P. grandidentata Mx. Large Poplar. Lvs. roundish-ovate, acute, with large, unequal, sinuate teeth, smooth, villous when young; bracts fan-shaped, 5-cleft, and silky-fringed. - Woods and groves, Can. and Nor. U. S. not uncommon. St. 40f high, with a diam. of If, straight, covered with a smooth, greenish bark. Branches distant, coarse and crooked, clothed with leaves only at their extremities, with terete twigs. Lvs. 3 to 5' long and nearly as wide, clothed with thick white down in spring, but becoming perfectly smooth. Aments 3 to •1' long, all the parts hairy, the sterile longer than the fertile. Stam. about 12, as in the preceding species. May.
5 P. heterophylla L. Cotton Tree. Branches terete; lvs. roundish-ovate, obtuse, uncinately serrate, cordate at base, the small auriculate lobes over-closed, white-tomentous when young, at length nearly smooth; ovaries with a long pedicel and conspicuous style. - Swamps, N. Eng. (rare) to I11. and La. A tree 40 to 60f high, trunk 1 to 2f diam. Lvs. 3 to 6' long, with small teeth, blunt or never acuminate at apex, and the base lobes often so overlapping as to conceal the insertion of the petiole. Apr., May.
5 P. balsamifeva L. Balsam: Poplar. Tacamehac. Branches terete; lvs. ovate, acuminate, with close-pressed serratures, white and reticulate-veiny beneath, glabrous both sides; bracts of the ament dilated, laciniate-fringed, slightly hairy; stam. 40 to 50. - Swamps and river banks, Me. to Penn., N. Y., Can. and the N. W. coast. A large tree, 40 to 80f high, trunk 1 to 2f diam. Lvs. 2 to 4' long. Sterile aments 2 to 3' long, fertile at length 4 to 6'. Stam. purple. Buds in spring covered with an aromatic rosin which may bo separated in boiling water.
7 P. candicans Ait. Balm OF Gilead. (Fig. 268, 269). Branches terete, lvs. ovate, cordate, acuminate, closely and unequally serrate, whitish and reticulate-veined beneath, petiole hirsute; bracts of the ament oval, laciniate-fringed; stam. about 20. - A fine tree of strong and peculiar fragrance, often cultivated, rarely growing wild, Can. and the Northern U. S. Height 30 to 50f, with a pyramidal head of dense ample foliage. Lvs. 4 to 6' long, at length smooth and dark green above. Sterile aments 2 to 3' long, fertile 4 to 6. Buds filled throughout with fragrant resin.
8 P. nigra L β. betulifolia Torr. Black Poplar. Young branches pubescent; lvs. deltoid-rhombic, conspicuously acuminate, finely crenate-serrate, smooth both sides; aments without hairs. - Trees 30 to 40f high, planted at Hoboken, N. J. and perhaps in Penn. † Eur. (P. betulifolia Ph. P. Hudsonica Mx.)
9 P. dilatata Ait. Lombardy Poplar. Lvs. smooth, acuminate, deltoid, serrate, the breadth equaling or exceeding the length; trunk lobed and sulcate. - Early brought to this country, and has been planted about many a dwelling and in village streets. Its rapid growth is the only commendable quality it possesses, while the huge worms by which it is often infested render it a nuisance, † Italy.
10 P. alba L. Abele. Silver-leap Poplar. Lva cordate, broad-ovate, lobed and toothed, acuminate, dark green and smooth above, very white-downy beneath; fertile aments ovate; stig. 4. - A highly ornamental, cultivated tree. Nothing can be more striking than the contrast between the upper and lower surface of the leaves, † Eur.