The Black Walnut (_J. nigra_) differs from the common kind, in the male flowers being on a smaller and more slender catkin, and furnished with a brown roundish bract at the back of the calyx. The female flowers are also in a sort of catkin, and four or five together. The fruit (see _a_ in _fig._ 78) is round, and the husk very thick at first, but it gradually wastes away, when the seed is ripe, instead of opening. The leaves have seven or more pairs of leaflets, which are generally nearly opposite, and sometimes they are without the terminal single leaflet, as shown at _b_. The shell of the nut is very hard, and the dissepiments, which are also very hard, are generally perfect, and divide the kernel into four parts. The nuts should be sown as soon as possible after they are ripe, as they will not keep good above six months. The tree grows above seventy feet high, and the wood is very hard and black. [Illustration: FIG. 79.—BUTTER-NUT (_Juglans cathartica_).] The Butter-nut (_J. cathartica_) resembles the Common Walnut in its male catkins, except that they are produced upon the old wood instead of being on the wood of the present year. The female flowers grow four or five together in a short catkin, and they are distinguished by their stigmas, which are rose-coloured. The fruit (_a_ in _fig._ 79) is pear-shaped, ending in a rather long point; and the kernel of the nut (_b_) resembles that of the Common Walnut, except in being more oily. The leaves (_c_) are like those of the Black Walnut, except that the leaflets are rather downy, and that there is a terminal one. The calyx of the female flower is also covered with a viscid down, which remains on the husk of the ripe fruit; and the shell of the nut is very hard and very much furrowed. The tree is of much smaller size than that of the Black Walnut, and it may be easily distinguished by the greyness of the bark of its young shoots; it also comes into leaf earlier, and the nuts are ripe about a fortnight sooner than the others. The wood is light, of a reddish colour, and rather a coarse grain. THE GENUS CARYA. [Illustration: FIG. 80.—THICK-SHELL BARK HICKORY (_Carya lacinosa_).]