SALICACEZ. 
SILVA OF NORTH AMERICA. 69 
POPULUS ACUMINATA. 
Cottonwood. 
Leaves rhomboid-lanceolate, long-acuminate, green on both surfaces; petioles 
slender, nearly terete. 
Populus acuminata, Rydberg, Bull. Torrey Bot. Club, xx. 
46, t. 149 (1893) ; Contrib. U. S. Nat. Herb. iii. 523. — 
Sargent, Silva N. Am. ix. 172.— Britton & Brown, Il. 
Fi. i. 491, £. 1167. — Britton, Man. 309. 
A tree, sometimes fifty or sixty feet tall, with a trunk three feet in diameter, but usually not more 
than forty feet in height, with a trunk from twelve to eighteen inches in diameter,' and stout spreading 
and ascending branches which form a compact round-topped or pyramidal head. The bark of young 
stems and of the large branches is smooth and nearly white, and on old trunks it is pale gray-brown, 
about half an inch thick and deeply divided into broad flat ridges. The branchlets are slender, terete 
or slightly four-angled, pale yellow-brown, and roughened for two or three years by the elevated oval 
horizontal leaf-scars which contain three dark fibro-vascular bundle-scars. The winter-buds are resinous, 
acuminate, and about a third of an inch in length, with six or seven light chestnut-brown lustrous scales, 
the lateral buds being much flattened by pressure against the branch. The leaves, which are pendulous 
on slender nearly terete petioles from one to three inches in length, are rhomboid-lanceolate, abruptly 
acuminate, gradually or abruptly narrowed and cuneate or concave-cuneate or rarely full and rounded 
at the mostly entire base, coarsely crenulate-serrate except near the apex, thick and leathery at maturity, 
dark green and lustrous on the upper surface, dull green on the lower surface, from two to four inches 
long and from three quarters of an inch to two inches wide, with slender yellow midribs, thin remote 
primary veins and obscure reticulate veinlets. The stipules are ovate, acute and apiculate or acuminate 
at the apex, about an eighth of an inch long, and caducous. The aments of flowers, which appear before 
the leaves, are slender, short-stalked, and from two to three inches in length, with scarious light brown 
glabrous scales dilated and irregularly divided at the apex into filiform lobes, and caducous. The 
numerous stamens, with short filaments and dark red anthers, are inserted on a wide oblique membra- 
naceous disk. The ovary is broadly ovate, gradually narrowed to the apex, which is crowned with 
large laciniately lobed nearly sessile stigmas and inclosed nearly to the middle in the deep cup-shaped 
disk which is persistent under the fruit. The fruiting aments are four or five inches long and the 
capsules are pedicellate, oblong-ovate, acute, thin-walled, slightly pitted, about a third of an inch long, 
and three or occasionally two-valved. The seeds are oblong-obovate, rounded at the apex, light brown, 
about one twelfth of an inch in length, and surrounded by long white hairs. 
Populus acuminata inhabits the banks of streams in the arid eastern foothill region of the Rocky 
Mountains and, although probably nowhere common, is distributed from Assiniboia’ to western Nebraska,’ 
eastern Wyoming,‘ and southern Colorado. Long confounded with Populus angustifolia, it was first 
distinguished by Mr. P. A. Rydberg,’ who found in 1891 a number of trees of this Cottonwood in 
Carter Cafion in Scott’s Bluff County, northwestern Nebraska. 
1 The wood specimen cut in northwestern Nebraska for the Jesup 
Collection of North American Woods in the American Museum of 
Natural History, New York, is twelve and a half inches in diame- 
ter inside the bark and only twenty-eight years old. The sapwood 
is two and three eighths inches thick, with sixteen layers of annual 
growth. 
2 Populus acuminata was collected by Mr. John Macoun at Leth- 
bridge, Assiniboia, June 5, 1894. 
8 Bessey, Rep. Nebraska State Board Agric., 1894, 104 ; 1899, 
85. 
4 See Nelson, Bull. No. 40, Wyoming Exper. Stat. 92 (Trees of 
Wyoming). 
5 Per Axel Rydberg (July 7, 1860) was born in Oth Parish, 
Westergoethland, Sweden, and was the son of a farmer. At the 
age of thirteen he was sent to the preparatory school of the Royal 
Gymnasium at Skara, and in 1881 was graduated from the Gymna- 
