i8o 



The Poplars 



Missouri, Nebraska, in the Rocky Mountains to New Mexico, and Chihuahua, 

 and in the Sierra Nevada to middle Cahfomia; it is reported to extend into Lower 



Cahfomia. The tree prefers sandy, gravelly, 

 or rocky soil, and attains a maximum height 

 of about 35 meters, with a trunk up to i me- 

 ter in diameter. 



Its branching is usually irregular, and the 

 branches sometimes droop at the ends; forms 

 are occasionally seen in which the branches 

 are decidedly pendulous. The bark, except 

 near the bases of old trees, where it is thick, 

 fissured, and nearly black, is rather thin, 

 nearly smooth and pale yellowish green or 

 yellowish brown. The young twigs are 

 greenish and loosely hairy, soon becoming 

 smooth, reddish brown and shining. The 



Fig. 138. American Aspen. 



buds are ovoid, pointed, a little sticky, about 

 7 mm. long, their scales shining. When 

 young the leaves are hairy-fringed, but quite smooth when mature, thin, dark 

 green and somewhat shining on the upper side, pale green on the lower; they are 

 ovate to nearly orbicular, finely and quite regularly toothed, with low, blunt teeth, 

 rather abruptly short-pointed, rounded or somewhat heart-shaped at the base, 2 

 to 6 cm. long and about as wide as long, or those of young plants much larger; 

 they quiver on their slender flat yellowish stalks in the hghtest breeze; the stip- 

 ules are narrow and nearly white. The catkins are 6 cm. long or less at flower- 

 ing time, or the pistillate ones longer; their scales are deeply 3-lobed or 5-lobed 

 and fringed with long hairs; there are 6 to 12 stamens in the staminate flowers; the 

 stigma-lobes of the pistillate flowers are linear. The conic capsules are pointed 

 and 5 to 6 mm. long. 



The American aspen is one of the first trees to reforest denuded slopes in the 

 north, its numerous seeds being widely spread by the wind and it grows rapidly. 

 The leaves turn yellow in the autumn and contribute much to the coloration of 

 the woods. Its wood is soft, weak, and soon decays; it is used in great quantities 

 for paper-pulp, is light brown in color, with a specific gravity of about 0.40. The 

 name tremuloides is with reference to the similarity of this tree to the European 

 aspen, Populus tremula Linnaeus. 



18. CERCIS-LEAVED ASPEN Populus cercidiphyUa Britton, new species 



This name is proposed for a tree, observed by Dr. C. C. Curtis in the Upper 

 Hoback basin, Wyoming, in August, 1900, which has foliage so different from 

 the American aspen that we think it must represent a distinct species. 



The twigs are smooth, the young shoots brown, becoming gray; tae resinous 



