Stone-fruits fall naturally into two distinct groups. In the first the leaves are rolled in the buds--convolute. The plums and the apricots belong to this section. In the buds of the other group the leaves are folded lengthwise along the midrib--conduplicate. To this section belong almonds, peaches and cherries. The two sections seem to be united in this matter of disposition of leaves in the bud, it should be said in passing, by a few species of American plums which are conduplicate in vernation. The second section is further subdivided by very marked differences in the fruits. The fruits of the peach and almond are larger than those of the cherry, less juicy,--in the case of the almond almost dry,--hirsute (except in the nectarine), and are borne without stems; and the blossoms usually appear long before the opening of the leaves. Cherry-fruits are always juicy, usually glabrous, and are borne on more or less distinct stems; and the blossoms appear with the leaves. Botanists who put these fruits in one genus usually redivide according to the characters given so that the plum and apricot stand in one sub-genus (Euprunus), the almond and peach in another (Amygdalus), and the cherry in a third (Cerasus). Differentiating more closely, we find that it is not so easy to distinguish between the peach and the almond. The likenesses are so many and so apparent that it is not to be wondered that Knight, whose theory we have discussed on a foregoing page, came to the conclusion that the peach is a modified almond, or that Darwin, with his belief that plants came sooner or later to express their environmental conditions, should be inclined to believe that the peach is an evolution from the almond. It is easy to imagine that countless ages ago--how long since is but an invitation to argue--the two species merged into one. Offspring of the parent-species once established in distinct soil and climatic conditions--the peach in China, the almond in southwestern Asia--differentiation began and in time each region was represented by a species of its own. Such an occurrence is but one of the commonplaces of evolution; but Knight, Lindley and Darwin thought they saw evidence that the separation came after the almond, the supposed parent-species, had been domesticated, the steps being from fleshy almond to bad clingstone, to good clingstone, to freestone, to nectarine. The arguments against such a descent have been given elsewhere.