Poplar (Fr. peuplier, from Lat. populus), the common name for trees of the genus populus, the classical Latin name, said to have been given because it was much planted in public walks and was regarded as the tree of the people. The willow family (salicacem) contains but two genera, salix, the willow, and the poplar; both dioecious trees, bearing their flowers in dense, cylindrical catkins, one under each scale or bract; the male flower consists of two to several stamens; the female of a one-celled ovary with numerous ovules, which ripens into a two-valved pod containing numerous seeds, furnished with long silky down. The poplars differ from the willows in having mostly angular branches, much broader and more or less heart-shaped leaves, and especially in the catkins, the scales of which in the willow are entire, but in the poplar are cut-lobed or fringed at the apex; the poplar has more numerous stamens, the stamens and the ovary in a small oblique cup or involucre; the scaly buds of the poplars are usually covered with a resinous varnish. They are natives of temperate countries, and of very rapid growth; their wood is soft, and of little use where strength is required, though very durable if protected from the weather; as a fuel the wood is exceedingly poor.
From their rapid growth and the ease with which they take root from cuttings, poplars of various kinds have been recommended for planting by settlers upon the prairies; but there are other trees which grow about as quickly, and produce wood in every respect more valuable. When the capsules are ripe they break open and set free the seeds, which by means of their downy tufts are scattered in multitudes in every direction; this down is not only exceedingly annoying to housekeepers, as it penetrates everywhere, but the particles floating in the air are breathed and cause much irritation of the air passages; if planted for shade, cuttings of the male trees should be selected to avoid the discomforts attendant upon the dispersion of the seeds. The leaves in most species are stirred by the slightest breath of wind, and may be seen in tremulous motion when the foliage of other trees is scarcely stirred; this motion is said to be due to the fact that the petioles are compressed laterally; in most leaves the flat surface of the petiole is parallel with the plane of the leaf blade, but in poplars it is at right angles to it.
The resinous material covering the unopened buds, more abundant in some species than others, is very useful to bees, as it furnishes them with a large share if not all of the propolis or cement with which on taking possession of a new hive they not only seal up every crack and crevice, but coat the whole interior surface. The species all contain a bitter principle, and the bark and leaves of several have been used as a tonic and an antiperiodic; they contain, besides salicine, an analogous principle, populine. The bark of some is used to dye a yellow. The most widely distributed and best known of our species is the cottonwood, populus monilifera, the necklace-bearing poplar, which is such a characteristic tree of the far west, that many suppose it to be a peculiarly western species; it is found in New England, and extends quite across the continent, being very abundant in the valley of the Mississippi, and on the otherwise treeless plains beyond is found marking the courses of rivers and small streams. It derives its specific name from the fruiting aments, which are very long, and with the unopened capsules upon them have some resemblance to a string of beads.
The tree grows 80 ft. or more high; the wood is very difficult to split, the fibres being so interlaced, and though of very poor quality, it is made, in localities where this is the only large wood procurable, to serve a variety of purposes. It is called cottonwood from the great abundance of down upon the seeds, and in planting it for shade special care should be taken to set cuttings from the staminate tree only. The narrow-leaved cottonwood, P. angustifolia, is a far western tree, found growing with the common cottonwood, and by some considered as a variety, as it resembles it in everything except its leaves, which are ovate-lanceolate, sometimes acute, and slightly serrate. The angled cottonwood, P. angulata, has more angular branches and larger leaves than the true cottonwood, and is supposed to be a mere variety of it; another form, known in the western states as yellow cottonwood, can only be distinguished by the color of its heart wood, which is yellowish; it splits more freely, warps much less, and is more durable than the ordinary cottonwood. - The American aspen, P. tremuloides, so named from its general resemblance to the European P. tremula, is a graceful tree 20 to 50 ft. high and quite common in woods, especially northward and in Canada; it shows in a marked degree the tremulous motion of the leaves, which are round-heart-shaped, with small regular teeth; the trunk has a smooth greenish white bark.
This is regarded as a short-lived tree of no special use. The large-toothed aspen, P. grandidentata, receives its name from the large, irregular, wavy teeth to its leaves, which are larger than in the one preceding, and, though smooth when full grown, are at first very downy on both sides; it is also a larger tree with a gray bark. Its timber, which has considerable strength, is durable if kept dry, and is employed for interior work; in states where it is abundant it is used for fences, being cut of the proper length, split, and nailed to posts; if felled in summer and peeled, it makes a durable fence stuff, but if left with the bark on it speedily decays. A weeping variety is known in the nurseries as P. grandidentata pendula; it has its branches as distinctly pendulous as those of the weeping willow, and when grafted upon a stock of Lombardy poplar, some 10 or 12 ft. high, it grows rapidly and makes one of the most beautiful of lawn trees. The downy poplar, P. heterophylla, has its leaves covered with white wool when young; it is a large tree of no special interest, found in swampy lands from New England to Illinois. The balsam poplar, P. balsamifera, is a large tree, also called tackmahack, found from New England to Wisconsin and northward; it has ovate, tapering, and pointed leaves, and the large leaf buds are covered with abundant varnish; the tree is of no special use.
Its variety called balm of Gilead (P. halsamifera, var. candi-cans) differs from the species in having broader and more or less heart-shaped leaves, with somewhat hairy petioles; it has a similar range with the preceding; it is rare in the wild state, but not uncommon in cultivation. Some 30 years ago it was a popular tree to plant for shade, and for the pleasant fragrance given off by its buds in spring; it suckers badly, and is much infested by insects. A tincture, made by putting the buds into spirit, was formerly a popular remedy for chronic rheumatism and pulmonary complaints; the resin of the buds is apparently a stimulant, similar to the turpentines and balsams. - Among the European species the most common in cultivation is the white poplar, P. alba, which is quite as frequently called abele, a name introduced with the tree from Holland into England; the Dutch name dbeel is said to be from the Latin albel-lus, whitish, a name given to the tree by some ancient writers. All these names refer to the marked character of the tree, the persistent white color of the under sides of the leaves; the white cottony down does not as in most species disappear with age, but as the leaves grow older the contrast between the dark green of the upper and almost snowy whiteness of the lower surface becomes stronger.
Cottonwood (Populus monilifera).
White Poplar or Abele (Populua alba).
The tree is a rapid grower; it has an ash-gray bark and a somewhat regular dense head; it was at one time very popular, but its defects having been discovered, it is now as much decried as it was formerly praised; in its appropriate place it is a most valuable tree, but that is not upon a lawn or in cultivated grounds, as it throws up suckers in great numbers; in paved streets, where suckers cannot grow, it is a desirable tree, as it thrives well in spite of dust and smoke; its suckering propensity makes it useful for planting near the seashore, to restrain the blowing sands. A variety of this (var. canescens), known as the gray poplar, has smaller leaves and not so white underneath; the wood is regarded as the most valuable of any European poplar, and is used for floors and other inside work, and for making various small articles; as a fuel it is about equal to pine. The black poplar, P. nigra, grows wild in southern Europe and temperate Asia, to the height of 50 to 80 ft., with an ample head and numerous branches. The bark is ash-colored, and becomes deeply furrowed with age; the leaves, slightly notched upon their edges, are pale green, the petioles yellowish.
The wood is soft, yellow, and fibrous, and is employed in making packing cases, and as it never splinters it is very useful for turning into bowls, trays, and such wares; it is an indifferent fuel. The bark is used in Russia in preparing morocco leather; the resin of the leaf buds is esteemed for healing properties. The Lombardy poplar, called P. dilatata and P. fastigiata, is believed to be a variety of the black poplar; it is well known for the upward tendency of its branches, and for its spire-like outline. About half a century ago there was a mania for planting this tree in avenues, than which nothing could be more formal or in worse taste; fortunately the abundant insect enemies of the tree have caused most of these sombre avenues to disappear, but a single tree is still occasionally seen. In landscape gardening, where it is desirable to give variety to the outline of a group, a specimen of this may be be introduced with good effect. The trembling poplar or European aspen, P. tremula, is a rapidly growing tree of middle size, with a clear, straight trunk, and smooth bark, becoming gray and cracking with age; the branches, which are few, become pendulous; the young shoots are tough, pliant, and of a reddish color; the flowers appear early; leaves roundish ovate or nearly orbicular and toothed, at first downy, but at length smooth on both sides.
The wood is tender and white, and employed by turners, engravers, cabinet makers, etc, and also used for burning into charcoal; its bark is employed for tanning; the leaves, either green or dry, are eaten readily by cattle and sheep. The tremulous character of the aspen (the older name of the tree is aspe, from A. S. cepse and asp) is recognized by many poets, and to " tremble like an aspen " has passed into a proverb. The tree is but little known in this country, it having no superiority to our native aspen.