Fig. 81.—The Willow (Salix). Fig. 81 shows the female flower of Salix fragilis at a, b is the honey gland, c the stigma, which is divided into four equal parts, and d the bract or scale with its hairy fringe; e is the male flower with its two stamens, two glands, and hairy scale. This species is a tall, bushy-headed tree, with the branches crossing each other frequently, being set on obliquely; and it is called the Crack Willow, from the young branches separating from the trunk in spring with the slightest blow or jerk, their bases being as brittle as glass. The leaves are of a deep green. The White Willow (Salix alba) differs from the preceding species in the branches being widely spreading and somewhat drooping, the old bark cracked into deep fissures, and the foliage of a silvery grey, owing to the silky hairs with which the leaves are more or less covered. The wood of the Tree Willows is soft and white, and very elastic; it is therefore used for cricket-bats, mallets, and other purposes where wood is wanted to resist a hard blow. S. vitellina, the Golden Osier, is so called from its golden-coloured bark; and S. purpurea, the Purple Willow, is so called from the colour of its branches. This last species has only one stamen; but as the anther is four-celled, it is probably two stamens grown together. All the species that have only one stamen have a four-celled anther, as for example the Rose Willow (S. Helix), which has the female catkins red. Salix caprea, the great round-leaved Sallow or Palm Willow, is perhaps the handsomest species, from the great abundance and golden hue of its flowers.
THE GENUS POPULUS.
Fig. 82.—Trembling Poplar or Aspen (Populus tremula).
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. candicans), which resembles the balsam Poplar, except in its leaves, which are very large and whitish on the under surface, and in the great rapidity of its growth, while that of the Balsam Poplar is rather slow.
BETULACEÆ.—THE BIRCH TRIBE.
The plants included in this tribe have single leaves, which are generally what is called feather-nerved; that is, the veins are marked strongly and deeply from the mid rib to the margin. The flowers are in cylindrical catkins, the male and female flowers being on the same plant.