is the great variability in the shape of the nuts, a feature that is much less marked in all the other sorts.
The white shell-bark occupies a sort of intermediate position in the genus. On one hand are the thick-shelled species already noted, forming one line, and on another line are two species marked in other ways, but mainly by a difference in the kernel. While in the three already described this is sweet and palatable, in these other two it is bitter and uneatable. These have, also, thin instead of thick husks, and they separate only about half-way down instead of into four distinct pieces. The shell is thin, so much so in some cases as to be easily crushed in the fingers. In size, shape, and markings there is none of the variability of the shell-bark. Of the two species the bitter-nut is
Fig. 4.—Bitter-nut (Carya amara).
the more common. The bark is close; the tree grows to be forty or fifty feet high, the shell is smooth, sharp-pointed, and marked with lines, while the kernel is so bitter that it is rejected by squirrels and other animals as long as other food can be obtained. The leaflets are small, from seven to nine in number. Its distribution is limited to nearly the same area as the mocker-nut, namely, the valleys of the Ohio and its tributaries, Minnesota, Kansas, and Western New York.
| Fig. 5.—Water-Hickory (Carya aquatica). | Fig. 6.—Small-fruited Hickory (Carya microcarpa). |
The water-hickory has many of the same features, but the shell of the nut is thinner still, and the kernel yet more bitter, while the tree is confined to the swamps of Carolina and Georgia, where it is by no means common. Its nut is of a reddish color, and more or less angular.
On a third line running from the white shell-bark are three other species. One of these is the small-fruited hickory, in which the husk and the shell are both thin, and the kernel, though small, is eatable. It is closely allied to the white shell-bark, and by some considered a
