POPLAR 511 bracteal scales ; the male flowers contain from eight to thirty stamens ; the fertile bear a one-celled (nearly divided) ovary, surmounted by the deeply cleft stigmas ; the two- valved capsule contains several seeds, each furnished with a long tuft of silky or cotton-like hairs. The leaves are broader than in most willows, and are generally either deltoid or ovate in shape, often cordate at the base, and frequently with slender petioles vertically flattened. Many of the species attain a large size, and all are of very rapid growth. The poplars are almost entirely confined to the north temperate zone, but a few approach or even pass its northern limit, and they are widely distributed within that area ; they show, like the willows, a partiality for moist ground, and often line the river-sides in otherwise treeless districts. The number of species cannot be very accurately denned, several, usually regarded as distinct, being prob ably merely variable forms of the same type. All yield a soft easily-worked timber, which, though very perishable when exposed to "weather, possesses sufficient durability when kept dry to give the trees a certain economic value. Of the European kinds, one of the most important and best marked forms is the White Poplar or Abele, P. alba, a tree of large size, with rounded spreading head and curved branches, which, like the trunk, are covered with a grey ish-white bark, becoming much furrowed on old stems. The leaves are ovate or nearly round in general outline, but with deeply waved, more or less lobed and indented margins and cordate base ; the upper side is of a dark green tint, but the lower surface is clothed with a dense Avhite down, which likewise covers the young shoots, giving, with the bark, a hoary aspect to the whole tree. As in all poplars, the catkins expand in early spring, long before the leaves unfold ; the ovaries bear four linear stigma lobes ; the capsules ripen in May. A nearly related form, which may be regarded as a sub-species, P. canescens, the Grey Poplar of the nurseryman, is distinguished from the true abele by its smaller, less deeply cut leaves, which are grey on the upper side, but not so hoary beneath as those of P. alba ; the pistil has eight stigma lobes. Both trees occasionally attain a height of 90 feet or more, but rarely continue to form sound timber beyond the first half- century of growth, though the trunk will sometimes endure for a hundred and fifty years. The wood is very white, and, from its soft and even grain, is employed by turners and toy-makers, while, being tough and little liable to split, it is also serviceable for the construction of packing cases, the lining of carts and waggons, and many similar purposes ; when thoroughly seasoned it makes good flooring planks, but shrinks much in drying, weighing about 58 Bt> per cubic foot when green, but only 33 Ib when dry. The white poplar is an ornamental tree, from its grace ful though somewhat irregular growth, and its dense hoary foliage ; it has, however, the disadvantage of throwing up numerous suckers for some yards around the trunk. The grey and white poplars are usually multiplied by long cuttings ; the growth is so rapid in a moist loamy soil that, according to Loudon, cuttings 9 feet in length, planted beside a stream, formed in twelve years trunks 10 inches in diameter. Both these allied forms occur throughout central and southern Europe, but, though now abundant in England, it is doubtful whether they are there indigenous. P. alba suffers much from the ravages of wood-eating larvae, and also from fungoid growths, especially where the branches have been removed by prun ing or accident ; trunks have occasionally acquired a diameter of 3 feet and upwards. The aspens form an important section, of which the Common Aspen of Europe, P. tremula, may be taken as the type, a tall fast-growing tree with rather slender trunk, and grey bark becoming rugged when old; the orbicular leaves, toothed on the margin, and slightly downy when young, are afterwards smooth, dark-green on the upper and greyish-green on the lower surface; the long slender petioles, much flattened towards the outer end, allow of free lateral motion by the slightest breeze, giving the foliage its well-known tremulous character. The aspen is an abundant tree in the northern parts of Britain, even as far as Sutherland, and is occasionally found in the coppices of the southern counties, but in these latter habitats seldom reaches any large size ; throughout northern Europe it abounds in the forests, in Lapland flourishing even in 70 N. lat., while in Siberia its range extends to the Arctic Circle ; in Norway its upper limit is said to coincide with that of the pine ; trees exist near the western coast having stems 15 feet in circumfer ence. The wood of the aspen is very light and soft, though tough ; it is employed by coopers, chiefly for pails and herring-casks ; it is also made into butchers trays, pack-saddles, and various articles for which its lightness recommends it ; sabots are also made of it in France, and in mediaeval days it was valued for arrows, especially for those used in target practice ; the bark is used for tanning in northern countries ; cattle and deer browse greedily on the young shoots and abundant suckers. Aspen wood makes but indifferent fuel, but charcoal prepared from it is light and friable, and has been employed in gunpowder manufacture. The powdered bark is sometimes given to horses as a vermifuge ; it possesses likewise tonic and febrifugal properties, containing a considerable amount of salicin. The aspen is readily propagated either by cut tings or suckers, but has been but little planted of late years in Britain. P. trepida, or tremuloides, is closely allied to the European aspen, being chiefly distinguished by its more pointed leaves ; it is a native of most parts of Canada and the United States, extending northwards as far as Great Slave Lake. The American Aspen is a smaller tree than P. tremula, seldom rising to a greater height than 30 feet, and rarely forming timber of any value ; the wood burns better in the green state than that of most trees, and is often used by the hunters of the north west as fuel; split into thin layers, it was formerly employed in the States for bonnet and hat making ; the bark is of some value as a tonic and febrifuge. P. yrandidentata, the Large-leaved American Aspen, is a tree of larger growth, with ovate or roundish leaves deeply and irregularly serrated on the margin. The wood is strong, and considered durable for indoor use ; it is also employed in some districts for fences ; split into slender strips, it has been applied to the manufacture of hats, like that of the Canadian aspen. Some of the most valuable trees of the genus belong to a section remarkable for the elongation of the fertile catkins, which become lax towards maturity. P. niyra, the Black Poplar, one of the most important of this group, is a tree of large growth, with dark deeply-furrowed bark on the trunk, and ash-coloured branches; the smooth deltoid leaves, serrated regularly on the margin, are of the deep green tint which has given name to the tree ; the petioles, slightly compressed, are only about half the length of the leaves. The black poplar is common in central and southern Europe and in some of the adjacent parts of Asia, but, though abundantly planted in Britain, is probably not there indigenous. The wood is of a yellowish tint. In former days this was the prevalent poplar in Britain, and the timber was employed for the purposes to which that of other species is applied, but has been superseded by P. monilifera and its varieties ; it probably furnished the poplar- wood of the Romans, which, from its lightness and soft tough grain, was in esteem for shield-making; in continental Europe it is still in some
request ; the bark, in Eussia, is used for tanning leather,