Page:Popular Science Monthly Volume 30.djvu/87

 variety only. A second species is the pig-nut, which has a thin husk but a thick shell. The kernel is small, and, though agreeable at first, soon becomes bitter and disagreeable. It is never eaten by man, but



used to feed hogs, or left for the wild animals. This nut is somewhat variable in shape, sometimes being distinctly pear-shaped and then again round. Michaux says that the same tree yields nuts as large as the thumb and others as small as the little finger. The third species in this same line is the nutmeg hickory, which has a somewhat rough husk, with a smooth nut, lined with streaks of white, and a shell so thick as to constitute one half of the whole nut. The kernel is inferior even to the pig-nut hickory.

If all these species were to be arranged so as to show their affinities, something like the following diagram would result:

From facts already given it will at once be apparent that two features in the nuts are correlated. The thick-shelled nuts have sweet kernels, though they differ in edibility, and the thin-shelled ones are invariably bitter. Thus the sweet ones protect their kernels by incasing them in hard shells—a precaution unnecessary for those whose kernels are bitter, because they are protected by this feature alone.

There remains, now, one species to be considered, and that is the pecan. While the white shell-bark seems to occupy a central place among the species, the pecan is intermediate between the hickories and the walnuts. These two genera, Carya and Juglans, as botanists know them, constitute the main part of the order to which they belong. When two genera are as closely allied as these are, an evolutionist accords a common origin to both. In fact, the difference between the two is a technical and comparatively an unimportant one.