Populus. SALICACE^E. 91 



2. POPULUS, Tourn. POPLAR. COTTONWOOD. ASPEX. 



Aments preceding the leaves, pendulous, axillary, sessile or nearly so, the pistil- 

 late longest and loosely flowered : bracts lacerately toothed or fringed. Stamens 

 few to many, inserted on the face of an obliquely truncate disk, with distinct filiform 

 filaments and purple anthers. Ovary surrounded by a more or less cup-shaped disk : 

 styles 2 to 4, often united at base, lobed or divided. Capsule ovate-oblong to glo- 

 bose, 2 - 4-valved. Trees with scaly and often resinous buds, caducous stipules, 

 and glandular-crenate leaves. Wesmael in DC. Prodr. xvi 2 . 323. 



About 20 species, of northern extra- tropical regions, equally divided between the Old and New 

 Worlds. The wood is light-colored, soft and light, durable if kept dry. The fragrant resinous bal- 

 sam, which coats abundantly the buds of some species, is occasionally collected for medicinal use. 



* Styles 2, with 2 or 3 linear lobes : capsules small, oblong-conical, thin, 2-valoed : 



stamens 6 to 20: leaves broadly ovate, crenulate ; petioles flattened. 



1. P. tremuloides, Michx. Trunk straight and slender, 20 to 50 feet high, 

 with smooth grayish-white bark ; branches not angled : buds long, viscid : leaves 

 round-ovate, 1 to 3 inches in diameter, very shortly acuminate, slightly cordate to 

 somewhat cuneate at base, villous-ciliate when young ; petioles slender, much flat- 

 tened above, as long as the blade : staminate aments dense, an inch or two long, 

 with long-ciliate bracts: stamens 7 to 10, Avith very short filaments: pistillate 

 aments 2 to 4 inches long, the rhachis pubescent : disk small : capsules on short 

 slender pedicels (a half to one line long), glabrous, 2 lines long : seed light brown, 

 a half line long. Michx. f. Arb. Amer. iii. 285, t. 8, fig. 1. 



From the Sacramento eastward across the continent and northward through British America to 

 the Arctic Ocean ; in the Rocky Mountains as far south as New Mexico. Usually in dense copses, 

 covering moist slopes and bottoms, at an altitude varying from 6,000 to 10,000 feet or more. 

 Generally known as " Quaking Asp." 



* * Styles 2 to 4, with dilated lobes : capsules large, snbylobose to ovate-oblong, 



2 - 4-valved, often thick. 



t Stamens usually 20 to 30 : leaves cordate or ovate to lanceolate, crenate ; 

 petioles terete : seed a line lony : -t/ouny bark brownish. 



2. P. trichocarpa, Torr. & Gray. A tree of open growth, 30 to 50 feet high 

 or more, with thick cracked bark, the young barren branches somewhat angled : 

 buds shining and viscid : leaves broadly ovate to oblong-lanceolate, acuminate, cor- 

 date (sometimes rounded) at base, 2 to 4 inches long, finely puberulent when young, 

 becoming somewhat lighter colored beneath ; petioles usually an inch or two long : 

 staminate aments dense, 2 inches long ; bracts slightly villous ; rhachis pubescent ; 

 disk broad, somewhat pubescent ; filaments as long as the anthers : pistillate aments 

 2 inches or more (becoming 6 inches) long, with pubescent rhachis, the bracts and 

 much dilated disk nearly glabrous : ovary densely pubescent ; styles 3, broadly di- 

 lated and lobed : capsules nearly sessile, subglobose, pubescent, 3-valved, 3 lines 

 in diameter : seed light-colored. Hook. Icon. t. 878 ; Watson, Bot. King Exped. 

 328, and Amer. Journ. Sci. 3 ser. xv. 136. P. balmmifera, var. y, Hook. Fl. Bor.- 

 Am. ii. 154. /'. balsamifera, var. (]) Calif ornicn, Watson, 1. c. 135. 



Var. cupulata, Watson, 1. c. 1 36. Disk of the pistillate flowers very large and 

 somewhat herbaceous, campanulate and twice longer than the ovary, pubescent : 

 bracts somewhat villous, and pedicels a line or two long. 



From San Diego northward to British Columbia and extending into Western Nevada : the vari- 

 ety from Plumas County, Mrs. Austin. According to Douglas it attains in Washington Territory 

 a height of 60 to 100 feet, with a diameter of 2 to 6 feet. Like the following species it is gen- 

 erally found scattered or in open groves along stream-banks and in river bottoms, at an altitude 

 not exceeding 6,000 feet. The narrow-leaved species of the Rocky Mountains (P. anc/tistifolia, 

 James) is found in the mountains of Central Nevada (Shoshone Mountains, Watson), and north- 

 westward to the valley of the Columbia. 



