The genus Carya (the Hickory) consists of ten or twelve species, which greatly resemble the Walnuts in their general appearance, but are distinguished by the male catkins, instead of being solitary, being produced in tufts or bunches, three or more on each peduncle. The stigma is also frequently four-lobed, and the husk, when ripe, divides into four equal valves, which in some of the species are very thick, as in the Thick-shell bark Hickory (see _a_ in _fig._ 80). The nut (_b_) is not valved, and it is either not furrowed, or very slightly so; but it has four angles which are more or less distinct in the different species: the shell and the dissepiments are both very hard, and the latter, as in the Mocker nut, are sometimes entire, so as to render it very difficult to extract the kernel. The leaves (_c_) resemble those of the walnut; but they are generally of a thinner texture, and somewhat downy, the down being disposed in little tufts, as may be seen by a microscope. The trees vary much in size, but all of them have a reticulated bark. The wood is of a coarse grain, and will not polish; but it is very strong, and so remarkably tough that it is hardly possible to break it. There is only one other genus in the order Juglandaceæ, and that consists of only a single species, _Pterocarya caucasica_. It has pinnate leaves of nineteen leaflets each, placed as closely as possible together; and the fruit, (that is, the husk,) is spread out on each side into a thin membrane or wing. This plant is sometimes called _Juglans fraxinifolia_. SALICACEÆ.—THE WILLOW TRIBE. The plants contained in this order have simple leaves, and the male and female flowers on different plants, both in upright cylindrical catkins. THE GENUS SALIX. The genus Salix (the Willow) contains perhaps more species than any other, above two hundred and fifty having been named and described, besides innumerable varieties. The plants included in the genus may, however, be all divided into three kinds—viz. the true Willows, which have thin green leaves, and which include all the tree species, most of which have brittle branches; the Osiers, the leaves of which resemble those of the Willows, but which are low shrubs with very tough branches; and the Sallows, the leaves of which are thick and woolly or shaggy. The Osiers and the true Willows are often confounded together; particularly when the former take, as they sometimes do, a tree-like character; but the Sallows are always perfectly distinct. The rods of the Osiers are used in basket-making.