3-5 mm. long and small cup-shaped disks 3-4 mm. in diameter; fruits ellipsoid- 

 ovoid, somewhat pitted, about 1 cm. long, 2- to 3-valved; seeds ellipsoid-obovoid, 

 about 2 mm. long. 



In canyons and valleys, about springs and water tanks, and along streams in 

 the Tex. s. and w. Trans-Pecos, N. M. (rather widespread) and Ariz. (Apache, 

 Navajo, Yavapai and Greenlee cos.) Apr.-June; from s. Alta., s. to Colo., Tex., 

 N.M. and Ariz. 



2. Populus angustifolia James. Narrowleaf cottonwood. Fig. 380. 



Tree to about 20 m. tall, with a slender trunk rarely more than 1.5 dm. in 

 diameter, the slender branches erect-ascending to form a narrow more or less 

 pyramidal crown; bark light-yellowish-green when young, shallowly fissured into 

 broad flat plates near base of old trunks; branchlets slender, light-yellowish-green 

 at first, later turning light-brown or orange-yellow and finally ashy-gray, glabrous 

 to somewhat pubescent; buds ovoid-conic to ellipsoid-conic, sharp-pointed, strongly 

 resinous, reddish-brown, glabrous to pubescent, 5-15 mm. long; leaf blades rather 

 thin but firm, bright-yellowish-green on the upper surface, much more pale-green 

 and sometimes puberulent on the lower surface, turning a dull-yellow in autumn, 

 lanceolate to occasionally narrowly ovate-lanceolate, gradually narrowed to the 

 acute to broadly obtuse apex, broadly to narrowly rounded or somewhat cuneate 

 at the base, the margins finely or coarsely serrate with numerous teeth, 4.5-15 cm. 

 long, 2-3.5 cm. wide; petioles short, semiterete, more or less horizontally flattened 

 and channeled on the upper side (especially near base of blades), puberulent to 

 subglabrous, usually much less than 2 cm. long, rarely longer; aments densely 

 flowered, narrowly cylindric, 4-7 cm. long; floral bracts broadly obovate, deeply 

 and irregularly lacerate at apex; staminate aments with subsessile or much- 

 abbreviated pedicels and deep cup-shaped oblique disks with reflexed margins, the 

 disks supporting 12 to 20 stamens; pistillate aments with abbreviated pedicels and 

 shallow cup-shaped disks, the ovary with 2 oblique dilated irregularly lobed 

 stigmas; fruits broadly ovoid to suborbicular, 4-7.5 mm. long, 2-valved; seeds 

 ovoid to obovoid, about 3 mm. long. 



In the area of distribution this species is found along streams usually above 

 3,500 ft. alt., rare in the Tex. Trans-Pecos, N. M. (rather widespread) and Ariz. 

 (Apache, Coconino and Yavapai cos.), Mar.-June; from s. Sask. and s. Alta., w. 

 to Wash., and Ore., s. to Tex., N.M. and Ariz.; also n. Mex. 



3. Populus Hinckleyana Correll. Fig. 381. 



Tree to 20 m. tall, with smooth light-gray bark which is deeply furrowed on 

 the lower part of the trunk and light-gray to tan-colored bark on the young growth; 

 twigs downy-puberulent, sometimes with some longer whitish spreading hairs; buds 

 ellipsoid, puberulent and resinous, orange-brown, 1-1.5 cm. long; leaf blades 

 rather thin, essentially glabrous or sometimes slightly puberulent on the margins 

 and on the veins on the lower surface, suborbicular-ovate to broadly deltoid-ovate, 

 truncate to broadly rounded at the base, acute to abruptly acuminate at the apex, 

 rather finely and irregularly (almost doubly) serrate on the margins (except at 

 the very base and apex), darker-green on the upper surface, to 7 cm. long and 

 6.5 cm. wide, usually smaller; petiole subterete, channeled or somewhat flattened 

 on the upper side, downy-puberulent, with age becoming glabrate. 2-4 (mostly 

 less than 3 ) cm. long; pistillate aments much-abbreviated, less than 5 cm. long, 

 with the rachis thick and rigid, the cup-shaped floral disks sessile and about 3 mm. 

 in diameter; fruits orbicular, pitted-rugose, 2-3 mm. in diameter, 2- to 3-valved; 

 seeds not fully developed in material examined. 



In canyons and floodplain areas in the Davis Mts. in the Trans-Pecos where it 

 is apparently endemic, Mar.-Apr. 



742 



