Poplar

P. euphratica, believed to be the weeping willow of the Scrip tures, is a large tree remarkable for the variability in the shape of its leaves, native to north Africa and western and central Asia.

In North America about 13 native species are found, together with some 15 well-marked varieties and some five or more hy brids, widely distributed throughout the continent. Most of these, especially the larger kinds, are generally called cottonwood.

The eastern cottonwood (P. deltoides), a very large, broad headed tree, with deeply-furrowed, grey or dark brown on the older trunks, which divide into many great arms, and large, ovate, finely toothed leaves, 4 to 7 in. long, longer than broad, occurs only locally and infrequently from Vermont to Mississippi. Its immensely more abundant variety, the common cottonwood or necklace poplar (P. deltoides var. virginiana), differs chiefly in having smaller triangular or ovate-triangular leaves, about as broad as long. It grows native from Quebec to North Dakota and south to Florida and Texas, sometimes attaining a height of 150 ft. and a trunk diameter of 8 feet. The loosely-flowered fruit ing aments form a pendent string, 6 to io in. long, of ripening pods, whence the name necklace poplar. The timber is used for soft lumber and pulpwood; and the tree is often planted for ornament. Numerous forms of this poplar are planted in Europe and America, probably mostly hybrids with forms of the Euro pean black poplar (P. nigra). Among these are the Carolina pop lar (P. canadensis), widely grown in streets and parks in the eastern States, a vigorous, upright tree, with strongly ascending branches, the trunk continuing through the top, and the Eugene poplar (P. canadensis var. Eugeni) which was originated in France in 1832. Both these forms bear only male flowers and hence do not produce the profusion of downy seeds which renders the common cottonwood somewhat objectionable as a street tree. The Norway or sudden-sawlog poplar, a very rapid-growing and hardy form, supposedly of Siberian origin, is probably either a variant of the common cottonwood or a hybrid of it. Since its distribution in 1904 from a Norwegian settlement in Minnesota it has been widely planted in the north-western States. In seven years the sudden-sawlog poplar will grow from a small cutting to a height of 5o ft. or more, and a trunk diameter of 6 to 8 in., producing quick shade, windbreaks, useful light timber and pulp wood.

As practically the only large tree in many parts of the interior region, where it grew along the watercourses, the cottonwood was utilized by the pioneers in an immense number of ways, but chiefly for soft lumber, fuel and quick shade. Its downy seeds, widely driven by the wind, readily take root in the wet sands of lake and river shores. Around the southern and eastern shores of Lake Michigan the cottonwood, because of this characteristic, is an important factor in the formation of dunes.

The swamp cottonwood or downy poplar

(P. lieterophylla),

which is found from Connecticut to southern Illinois and south ward to Florida and Louisiana, attains a height of go ft. and trunk diameter of 3 feet. It has dark rough bark and large broadly ovate leaves, 5 to 6 in. long, which are intensely woolly when young. This tree furnishes excellent pulpwood and the lumber known to the trade as black poplar.

The black cottonwood (P. trichocarpa), the largest broad-leaved tree indigenous to the Pacific coast region of North America, attains a height of 200 ft. and a trunk diameter of 8 feet. It grows from Alaska to Lower California and eastward to Idaho and Nevada. It has yellowish, fissured bark and large ovate, finely-toothed leaves, 2 to II in. long, lustrous green above and whitish below. The timber is utilized for wooden ware and pulp wood.

The balsam poplar or tacamahac

(P. balsamifera), the "liard" of the Canadian, voyageurs, is a narrow-topped tree, sometimes Ioo ft. high, with a diameter of 7 ft. at the stump. It has smooth grey bark ; ovate, pointed, dark-green leaves, which are whitish below, and resinous buds with a pleasing balsamic odour. It is found along the northern border of the United States from Maine westward, southward in mountains to Colorado, Nevada and Ore gon, and northward nearly throughout Canada and Alaska to the Arctic circle. Like the cottonwood in the United States, the taca mahac was put to manifold uses by the early settlers in the prairie regions of Canada. The balm-of-gilead poplar (P. can dicans) is similar to but smaller than the balsam poplar, with broad, heart-shaped leaves and very large, resinous, highly aro matic buds. It is widely planted in the north-eastern States and Canada, and also occurs as if native. It is thought to be a hybrid of European origin but perhaps partly of North American par entage.

In the Rocky Mountain region and adjacent plains are found the lance-leaf cottonwood (P. acuminata), the narrow-leaf cot tonwood (P. angustifolia) and a foot-hill species (P. Sargenti). In the arid districts of the south-western States there are seven species of cottonwood, all of more or less limited range, among which are the Fremont cottonwood (P. Frernonti) and the Mexi can cottonwood (P. Wislizeni).

The white, the black, and the Lombardy poplar are widely planted in the eastern States and Canada, where the two first named have become more or less naturalized.

In 1925 the cut of cottonwood lumber in the U.S.A. was 142, 113,000 bd.ft., valued at $3,794,000, lumbered chiefly in the Mis sissippi valley, mostly from the common cottonwood in the North and swamp cottonwood in the South. In 1936 it was 137,000,00o bd.ft., valued at $2,633,000. (See ASPEN.) See C. S. Sargent, Manual of the Trees of North America (19o5, 2nd ed. 1922) ; G. B. Sudworth, Forest Trees of the Pacific Slope (1908) and Check List of the Forest Trees of the United States (1927) ; L. H. Bailey, Manual of Cultivated Plants (1924).