SWEET-GALE FAMILY 69 



The short, tortuous stems of this willow form a depressed 

 body only 1 to 4 in. high and the flowering 1 shoots rarely ex- 

 ceed 6 in. It is a common inhabitant of moist slopes near 

 timber-line, often growing entangled with other alpine dwarfs 

 and sedges. 



12. S. monica Bebb. Mono Willow. Leaves oblong or 

 oblanceolate, acute at each end (or the lower obtuse), entire 

 or nearly so, % to 1*4 i n - long* glabrous or lightly pubescent 

 around apex; stipules none. Catkins small, roundish, sessile 

 or on a very short 2-bracted peduncle. Capsules sessile, 

 sparsely silky. — Mono Pass, Mt. Dana, Tuolumne Meadows, 

 Rancheria Mt., etc., occurring as a low, profusely branched 

 shrub, the lower branches reclining but not creeping. The 

 Common Cottonwood (P. fremontii) replaces this species in 

 the Sacramento and San Joaquin valleys. 



2. POPULUS. Poplar. 

 Trees, similar to willows but with mostly broader leaves. 

 Buds covered by several scales. Scales of the catkins as 

 though torn. Stamens numerous. Stigmas long. 



1. P. trichocarpa T. & G. Black Cottonwood. Leaves 

 ovate or lanceolate, truncate or heart-shaped at base, acute, 

 finely toothed, 2 to 5 in. long, on petioles ^2 to 2 in. long, 

 green above, brown or whitish beneath. 



The Black Cottonwood becomes a conspicuous, broad- 

 topped tree along the rivers in Hetch Hetchy, Yosemite, and 

 Wawona valleys. The bark is whitish and smooth at first, 

 but fissured on old trunks into long, narrow plates. 



2. P. tremuloides Michx. Aspen. Leaves round-ovate or 

 orbicular, abruptly tipped, faintly toothed, Y\ to 2J^ in. long, 

 on petioles }£ to 2 in. long. 



The Aspen is a slender, graceful tree with leaves constantly 

 quivering even when there is apparently no breeze, the flat 

 petiole being specially adapted to ease of movement. The 

 bark is greenish white, becoming black. No other American 

 tree has so wide a range as the Aspen, which grows from 

 Hudson Bay and the Arctic regions south to Tennessee and 

 Mexico. In our district it grows on moist slopes and along 

 streams, forming thickets or small groves. It belongs to the 

 Upper Coniferous Belt, rarely descending to 4500 ft. 



MYRICACEAE. Sweet-gale Family. 

 Shrubs and small trees with alternate simple leaves without 

 stipules. Flowers in short catkins, without calyx or corolla. 



