5. Populus Acuminata Rydberg. Black Cottonwood

Fig. 1444

P. acuminata Rydberg, Bull. Torr. Club 20: 50. 1893.

Populus coloradcnsis Dode, Mem. Soc. Hist. Nat. Autun 18: [reprint 58]. 1905.

A slender tree, with terete twigs, reaching approximately the dimensions of the preceding species, the crown broadly pyramidal with spreading branches, the foliage glabrous. Leaves rhomboid-lanceolate, spreading or drooping, drying green, abruptly or gradually long-acuminate at the apex, cuneate, obtuse or rounded at the base, 2-6' long, 1'-2 1/2' wide, crenulate or the base entire; petioles slender, 1'-2 1/2' long; staminate aments about 1 1/2' long; pistillate aments slender, drooping, 3-5' long; capsules ovoid, obtuse, distinctly pedicelled.

Borders of lakes and streams, North Dakota to As-siniboia, western Nebraska, New Mexico and Nevada. April-May.

6. Populus Heterophylla L. Swamp Or Downy Poplar

Fig. 1445

Populus heterophylla L. Sp. PI. 1034. 1753.

An irregularly branching tree, sometimes 80° high and with a trunk 30 in diameter, the bark rough. Young foliage densely tomentose. Leaves long-petioled, broadly ovate, obtuse or subacute at the apex, rounded, truncate or subcordate at the base, crenulate-denticulate, 5'-6' long, or those of young plants much larger, glabrous or somewhat floccose beneath when mature; petioles terete; bracts glabrous or nearly so; staminate aments stout, 3'-4' long, 9"-12" in diameter, drooping; stamens numerous; pistillate aments raceme-like, peduncled, erect or spreading, loosely flowered; capsules ovoid, acute, 2-valved, 4"-6" long, shorter than or equalling their pedicels.

In swamps, Connecticut to Georgia, west to Louisiana, north in the Mississippi Valley to Ohio, Indiana, Mis-souri and Arkansas. Wood soft, weak, compact, brown, weight per cubic foot 26 lbs. River- or swamp-cotton-wood. Balm-of-gilead. April-May.

7. Populus Grandidentata Michx. Large-Toothed Aspen

Fig. 1446

Populus grandidentata Michx. Fl. Bor. Am. 2: 243. 1803.

A forest tree with smooth, greenish-gray bark, maximum height about 75°, and trunk diameter 2 1/2°. Leaves ovate-orbicular, those of very young plants densely white-tomentose beneath, sometimes 10 long, with irregularly denticulate margins, those of older trees tomentose when young, glabrous when mature, short-acuminate, coarsely undulate-dentate, obtuse or truncate at the base, 2 1/2'-4' long; petioles slender, flattened laterally; bracts silky, irregularly 4-7-cleft; staminate aments 2-4' long, about 5" in diameter, drooping; pistillate aments somewhat pubescent, dense, 3-5' long in fruit, also drooping; stigma-lobes narrow; capsule conic, acute, 2-valved, about 3" long, rather less than 1" in diameter, papillose.

In rich woods, Nova Scotia to Ontario and Minnesota, south to Delaware. North Carolina and Tennessee. Wood soft, weak, light brown, compact; weight per cubic foot 29 lbs. White poplar. April.