The genus Populus (the Poplar) is distinguished from Salix by the bracts of the flowers being deeply cut instead of being entire; by both the male and female flowers having a calyx; and by the male flowers never having less than eight stamens. The leaf-buds are also covered with numerous scales. _Fig._ 82, _a_, shows the stamens of the Trembling Poplar or Aspen (_Populus tremula_) shrouded in their cup-like calyx, and with their laciniated bract; _b_ shows the female flower with its four stigmas and deeply-cut bract; and _c_, the pod with its valves curling back, so as to show the downy covering of the seeds. All these parts are magnified to show them distinctly, as they are nearly the same in all the species. The following are the distinctions between the principal species. In the White Poplar, or Abele-tree (_P. alba_), the leaves are lobed, and covered with a white down on the under side. In _P. canescens_, the Grey Poplar, the leaves are also downy beneath; but they are roundish, and the female flower has eight stigmas instead of four. The Aspen (_P. tremula_) has four stigmas, with two leafy appendages at the base, which look like two other stigmas; and the petioles of the leaves, which are very long, are flattened, and so attached to the stem as to be twisted by the weight of the leaf when acted upon by the wind, which gives them their tremulous motion: these leaves are smooth on both sides. All these species have spreading roots, and send up a great many suckers; and their wood is used for butchers’ trays, pattens, bowls, milk-pails, and various other purposes. _Populus nigra_, the Black English Poplar, on the contrary, does not send up suckers, and its wood is of very little use; it is, however, very ornamental from the large size and great number of its male catkins, and the bracts of the flowers being of a brownish red, which gives them, when fallen, the appearance of the large brownish-red caterpillars of the Goat-moth. The Black Italian Poplar (_P. monilifera_) is remarkable for the quickness of its growth. The capsules of the female trees contain such a quantity of down attached to the seeds, as to render it quite unpleasant to walk under them when they are ripe. The Lombardy Poplar (_P. fastigiata_ or _dilatata_) is remarkable for its upright and close habit of growth; its leaves also are very peculiar in their shape, being broad at the base and then tapering suddenly to a point. The seeds resemble those of the Black Italian Poplar in the quantity of wool which they produce, but luckily the female plants are extremely rare. There are many other species, the most remarkable of which are the Carolina Poplar (_P. angulata_), known by its square stem and very large leaves; the Balsam Poplar, or Tacamahac tree (_P. balsamifera_), the buds of which are covered with a resinous fragrant substance, and the leaves are of a pale yellowish green, appearing very early in spring; and the Ontario Poplar (_P.