TREES OF NORTH 



AMERICA 



160 



in their second, and ultimately ashy gray. "Winter-buds very resinous, ovate, long- 

 pointed, covered hy usually 5 thin concave chestnut-brown scales, the terminal 

 i'_^' long and nearly twice as large as the axillary buds. Bark f '-!' thick, light 

 yellow-green, divided near the base of old trees by shallow fissures into broad flat 

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

 sapwood of 10-30 layers of anqyp growth. ,r 



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 andNew Mexico and southern Arizona; the common Cot- 

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

 Idaho. 



6. Populus acuminata, Rydb. Cottonwood. 



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. Flowers: 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 



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 -fa' 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 brauchlets roughened for two or three years by 



