SALICACES. SILVA OF NORTH AMERICA. 159 
on the margins with long pale caducous hairs, and at maturity are thin and firm in texture, dark green 
and lustrous on the upper surface, pale dull yellow-green on the lower, and from an inch and a half to 
two inches in length and breadth, with yellow nerves raised and rounded on the upper side and slender 
veins forked and united near the margins and connected by reticulate veinlets more prominent above 
than below; they are borne on slender yellow petioles compressed laterally and from an inch and a half 
to three inches in length, and turn bright clear yellow in the autumn before falling, when they leave 
small three-lobed leaf-scars. The stipules of the first leaves resemble the inner bud-scales ; higher on 
the branch they are linear-lanceolate, white and scarious, about half an inch long, and caducous. The 
flower aments appear in very early spring and vary from one and a half to two and a half inches 
in length; their scales are deeply divided into from three to five linear acute lobes fringed with long 
soft gray hairs. The stamens vary from six to twelve in number, and are inserted on the disk, which is 
oblique, with entire margins. The ovary is conical, crowned by a short thick style and two erect 
stigmas thickened and club-shaped below and divided above into linear divergent lobes, and sur- 
‘rounded at the base by the broad oblique slightly crenate disk, which is persistent under the fruit. 
The capsules mature in May and June, when the fruiting ament, which has a slender pubescent or 
tomentose rachis, is about four inches in length; they are oblong-conical, light green, thin-walled, and 
nearly a quarter of an inch long. The seeds are obovate, light brown, about one thirty-second of an 
inch in length, and surrounded with long soft snowy white hairs. 
Populus tremuloides, which is the most widely distributed tree of North America, ranges from 
southern Labrador to the southern shores of Hudson’s Bay, thence northwesterly nearly to the mouth 
of the Mackenzie River and the valley of the Yukon River in Alaska,’ southerly through the north- 
ern states to the mountains of Pennsylvania, northeastern Missouri? and southern Nebraska,* and 
through all the mountain regions of the west, where it often ascends to elevations of ten thousand 
feet above the level of the sea, to the Sierras of central California,’ northern Arizona and New Mexico, 
the high mountain ranges of Chihuahua, and San Pedro Martir Mountain in Lower California.» The 
Aspen rarely exceeds a height of fifty feet in eastern Canada and the northeastern states, where 
it is a generally distributed and common tree, preferring rather moist sandy soil and gravelly hill- 
sides and growing most luxuriantly near the borders of swamps and open forest glades. On the 
western margin of the Atlantic forest north of the forty-ninth degree of latitude it grows beyond 
the Spruces and Larches of the east, and borders the mid-continental prairie region with a belt of 
varying width; in this prairie region, outside the river-valleys, which it does not enter, the Aspen 
grows with its greatest vigor and to its largest size, indicating by its presence soil suitable to the pro- 
duction of cereal crops; farther to the northwest it forms with the Birch and the Spruce the forests 
of the high ridges, but does not invade the flood plain of rivers or their islands. In the west and 
southwest it grows, on the high slopes of mountains and along the banks of streams, and is usually not 
large, although individuals a hundred feet tall sometimes occur. 
The wood of Populus tremuloides is close-grained but soft, and neither strong nor durable; it 
contains numerous very thin hardly distinguishable medullary rays and numerous minute scattered open 
ducts, and is light brown, with nearly white sapwood composed of from twenty-five to thirty layers of 
annual growth, and sometimes six or seven inches in thickness. The specific gravity of the absolutely 
dry wood is 0.4032, a cubic foot weighing 25.13 pounds. In the east it is largely manufactured into 
wood-pulp for the manufacture of paper, and in the west is occasionally employed for floormg and in 
1 Provancher, Flore Canadienne, ii. 532. — Brunet, Cat. Vég. Lig. 6 Macoun, Trans. Roy. Soc. Can. xii. 6. 
Can. 55. — G. M. Dawson, Can. Nat. n. ser. ix. 331.— Bell, Rep. 7 On the slopes of the San Francisco Mountains in northern Ari- 
Geolog. Surv. Can. 1879-80, 45°. — Macoun, Cat. Can. Pl. 456. zona, at elevations of seven or eight thousand feet above the level of 
2 Bush, Rep. State Hort. Soc. Missouri, 1895, 360. the sea, Aspens nearly a hundred feet in height with gleaming white 
8 Bessey, Rep. State Board Agric. Nebraska, 1894, 103. trunks from two to three feet in diameter near the ground are not 
4 Hansen, Flora of the Sequoia Region, 11. uncommon. 
5 Brandegee, Zoé, iv. 209. 
