Leaves lanceolate, ovate-lanceolate, elliptic or rarely obovate, narrowed to the tapering acute or rounded apex, gradually narrowed and cuneate or rounded at base, finely or on vigorous shoots coarsely serrate, thin and firm, bright yellow-green above, glabrous or rarely puberulous and paler below, 2′—3′ long, ½′—1′ wide, or on vigorous shoots occasionally 6′—7′ long, and 1½′ wide, with a stout yellow midrib and numerous slender-oblique primary veins arcuate and often united near the slightly thickened revolute margins; petioles slender, somewhat flattened on the upper side, and in falling leaving small nearly oval obcordate scars. Flowers: aments densely flowered, glabrous, short-stalked, ½′—2½′ long, the pistillate becoming 2½′—4′ long before the fruit ripens; scales broadly obovate, glabrous, thin, scarious, light brown, deeply and irregularly cut into numerous dark red-brown filiform lobes; disk of the staminate flower cup-shaped, slightly oblique, short-stalked; stamens 12—20, with short filaments and large light red anthers; disk of the pistillate flower shallow, cup-shaped, slightly and irregularly lobed, short-stalked; ovary ovoid, more or less 2-lobed, with a short or elongated style and 2 oblique dilated irregularly lobed stigmas. Fruit broadly ovoid, often rather abruptly contracted above the middle, short-pointed, thin-walled, 2-valved; pedicels often ⅓′ long; seeds ovoid or obovoid, rather obtuse, light brown, nearly ⅛′ long. A tree, 50°—60° high, with a trunk rarely more than 18′ in diameter, slender erect branches forming a narrow and usually pyramidal head, and slender glabrous or rarely puberulous branchlets marked by pale lenticels, at first light yellow-green, becoming bright or dark orange color in their first season, pale yellow in their second winter, and ultimately ashy gray. Winter-buds very resinous, ovoid, long-pointed, covered by usually 5 thin concave chestnut-brown scales; terminal ¼′—½′ long and nearly twice as large as the axillary buds. Bark ¾′—1′ 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 annual growth. Distribution. Banks of streams usually at altitudes of 5000°—10,000° above the sea; southern Alberta to the Black Hills of South Dakota and northwestern Nebraska (basin of Hat Creek) westward through Wyoming, Montana and Idaho to Yakima County, Washington, and southward to central Nevada, southwestern New Mexico (Silver City, Grant County) and northern Arizona; the common Cottonwood of northern Colorado, Utah, Wyoming, southern Montana, and eastern Idaho; on the mountains of Chihuahua. 7. Populus acuminata Rydb. Cottonwood. [Illustration: Fig. 122]