POPLAR (________), the name of a small group of arborescent amentneeous plants, belonging to the order ,S'alicaceze. The catkins of the poplars differ from those of the nearly allied willows in the presence of a rudimentary perianth, of obliquely cup-shaped form, within the toothed 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 inost 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 defined, - 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 sterns. 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 white 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. caneA,ens, 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 ihose 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-inakers, 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 th per cubic foot when green, but only 34 lb when dry. The white poplar is an ornamental tree, from its gra,ce-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, (rivino. the foliao.e 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 liinit 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-ca,sks ; it is also made into butchers' trays, pack-saddles, and various cuticles for which its lightness recommends it ; sabots are also made of it in France, and in inediwval 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 sonietimes 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. tienivia, seldom rising to a greater height than 30 feet, and rarely forniing 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 yalue as a tonic and febrifuge. P. grandidentata, 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 becoine lax towards maturity. P. nigra, 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 niargin, 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 tiniber 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 Russia, is used for tanning leather, while in Kamchatka it is sometimes ground up and mixed Nvith meal ; the gum secreted by the buds was employed by the old herbalists for various medicinal purposes, but is probably nearly inert ; the cotton-like down of the seed has been converted into a kind of vegetable felt, and has also been used in paper-making. A closely related form is the well-known Lombardy Poplar, P. fastirliata, remark-able for its tall cypress-like shape, caused by the nearly vertical growth of the branches. Probably a mere variety of the black poplar, its native land appears to have been Persia or some neighbouring country; it was unknown in Italy in the days of Pliny, while from remote times it has been an inhabitant of Kashmir, the Punjab, and Persia, where it is often planted along roadsides for the purpose of shade; it was probably brought from these countries to southern Europe, and derives its popular name from it,s abundance along the banks of the Po and other rivers of Lombardy, where it is said now to spring up naturally from seed, like the indigenous black poplar. It was introduced into France in 1749, and appears to have been grown in Germany and Britain soon after the middle of the last century, if not earlier. The Lombardy poplar is valuable chiefly as an ornamental tree, its timber being of very inferior quality; its tall erect growth renders it use-ful to the landscape-gardener as a relief to the rounded forms of other trees, or in contrast to the horizontal lines of the lake or river-bank where it delights to grow. In Lombardy and France tall hedges are sometimes formed of this poplar for shelter or shade, while in the suburban parks of Britain it is serviceable as a screen for hiding buildings or other unsightly objects from view; its growth is extremely rapid, and it often attains a height of 100 feet and upwards, while from 70 to 80 feet is an ordinary size in favourable situations.
P. canialcusis, the " Cotton-wood" of the western prairies, and its Yarieties are perhaps the inost useful trees of the germs, often forming almost the only arborescent vegetation on the great American plains. The I'. canaciensis of Michaux, which may be regarded as the type of this group, is a tree of rather large growth, with rug,ged grey trunk, and with the shoots or young branches more or less angular ; the glossy deltoid leaves are sharply pointed, somewhat cordate at the base, and with flattened petioles ; the fertile catkins ripen about the middle of June, when their opening capsules discharge the cottony seeds which have given the tree its common western name ; in New England it is sometimes called the " River Poplar." The cotton-wood timber, though soft and perish-able, is of value in its prairie habitats, where it is frequently the only available wood either for carpentry or fuel ; it has been planted to a considerable extent in some parts of Europe, but in England a kindred form, P. monilifera, is generally preferred from its larger and more rapid growth. In this well-known variety the young shoots are but slightly angled, and the branches in the second year become round; the deltoid short-pointed leaves are usually straight or even rounded at the base, but sometimes are slightly- cordate ; the capsules ripen in Britain about the middle of May. This tree is of extremely rapid growth, and has been known to attain a height of 70 feet in sixteen years ; the trunk occasionally acquires a dia-meter of from 3 to 5 feet, and, according to Emerson, a tree near 2,:ew Ashford, Massachusetts, measured 20 feet 5 inches in circum-ference ; it succeeds best in deep loamy soil, bat will flourish in nearly any inoist but well-drained situation. The timber is much used in some rural districts for flooring, and is durable for indoor pur-poses when protected from dry-rot ; it has, like most poplar woods, the property of resisting fire better than other timber. The native country of this sub-speeies has been much disputed ; but, though still known in many British nurseries as the " Black Italian Pop-lar," it is now well ascertained to be an indigenous tree in many parts of Canada and the Sta,tes, and is probably a mere variety of earualensis ; it seems to have been first brought to England from Canada in 1772. In America it seldom attains the large size it often acquires in England, and it is there of less rapid growth than the prevailing form of the western plains ; the name of "cotton-wood" is locally given to other species. 1'. macrophylla or candi-cam., commonly known as the Ontario Poplar, is remarkable for its very large heart-shaped leaves, sometimes I() inches long ; it is found in New England and the milder parts of Canada, and is frequent15- planted in Britain ; its growth is extremely rapid in moist land ; the buds are covered with a balsainie secretion. The true Balsam Poplar, or Taeamalme, P. balsamifera, abundant in most parts of Canada and the northern States, is a tree of rather large groNvth, often of somewhat fastigiate habit, w ith round shoots and oblong-ovate sharp-pointed leaves, the base never cordate, the petioles round, and the disk deep glossy green above but somewhat downy below. This tree, the "Bard" of the Canadian voyageur, abounds on many of the river sides of the north-western plains ; it occurs in the neighbourhood of the Great Slave Lake and along the Mackenzie river, and forms inuch of the drift.wood of the Arctic coast. In these northern habitats it attains a large size ; the wood is very soft ; the buds yield a gum-like balsam, from which the eomino» name is derived ; considered valuable as an antiscorbutic, this is said also to have diuretic properties ; it was formerly iinported into Europe in small qnantities, under the name of " baurne focot," being scraped off in the spring and put into shells. This balsam gives the tree a fragrant odour when the leaves are unfolding. The tree grows well in Britain, and acquires occasion-ally a considerable size. A very closely allied variety abounds in Siberia and Dauria, chiefly distinguished by its wider leaves, rounded growth, and the darker tint of its wood ; kind of wine, esteemed as a diuretic, is prepared in Siberia from the buds. Its fragrant shoots and the fine yellow green of the young leaves recommend it to the ornamental planter. It is said by Aiton to have been intro-duced into Britain about the end of the 17th century. (C. P. J.)