160 



TREES OF NORTH AMERICA 



ill their second, and nltiniatoly ashy gray. "Winter-buds very resinous, ovate, long- 

 pointed, covered by usually o thin concave chcstuut-hrown scales, the terminal 

 \'-^' long and nearly twice as large as the axillary buds. Bark ^'-V thick, light 

 yellow-green, divided near the base of old trees by shallow fissures into bnxid Hat 

 ridges, smooth and much thinner above. Wood light brown, with thin nearly white 

 sapwood of 10-30 layers of annual growth. 



Distribution. Banks of streams usually at elevations of 5000-10,000 above 

 the sea; southwestern Assiniboia to the Black Hills of Dakota and northwestern 

 Nebraska, and southward along the mountain streams of the interior of the conti- 

 nent to central Nevada and New Mexico and southern Arizona; the common Cot- 

 tonwood of northern Colorado, Utah, Wyoming, southern Montana, and eastern 

 Idaho. 



6. Populus acuminata, Rydb. CottonTvood. 



Leaves rhombic-lanceolate, abruptly acuminate, gradually or abruptly narrowed 

 and cuneate or concave-cuneate, or rarely broad and rounded at the mostly entire 

 base, coarsely crenately serrate except near the apex, dark green and lustrous above, 

 dull green below, 2'-4' long, |'-2' wide, with slender yellow midribs, thin remote 

 primary veins and obscure reticulate veinlets; their petioles slender, nearly terete, 

 l'-3' long. Flo"wers: aments slender, short-stalked, 2'-3' long, the pistillate becom- 

 ing 4' or 5' long before the fruit ripens, their scales scarious, light brown, glabrous, 

 dilated and irregularly divided into filiform lobes; disk of the staminate flower wide, 

 oblique, and membranaceous; stamens numerous, with short filaments and dark red 

 anthers ; disk of the pistillate flower deep cup-shaped ; ovary broadly ovate, gradually 



ti(>- !34 



narrowed above, with large laciniately lobed nearly sessile stigmas. Fruit pedicel- 

 late, oblong-ovate, acute, thin- walled, slightly pitted, about \' long, 3 or rarely 

 2-valved; seeds oblong-obovate, rounded at the apex, light brown, about ^' in 

 length. 



A tree, usually about 40 high, with a trunk 12'-18' in diameter, stout spreading 

 ascending branches forming a compact round-topped head, and slender terete or 

 slightly 4-angled pale yellow-brown branchlets roughened for two or three years by 



