ich differ
more in the flower than in fruit. If, as is highly probable, the peach is
the modified descendant of the almond, a surprising amount of change has
been effected in the same species, in the fleshy covering of the former and
in the kernels of the latter.

When parts stand in such close relation to each other as the fleshy
covering of the fruit (whatever its homological nature may be) and the
seed, when one part is modified, so generally is the other, but by no means
necessarily in the same degree. With {219} the plum-tree, for instance,
some varieties produce plums which are nearly alike, but include stones
extremely dissimilar in shape; whilst conversely other varieties produce
dissimilar fruit with barely distinguishable stones; and generally the
stones, though they have never been subjected to selection, differ greatly
in the several varieties of the plum. In other cases organs which are not
manifestly related, through some unknown bond vary together, and are
consequently liable, without any intention on man's part, to be
simultaneously acted on by selection. Thus the varieties of the stock
(Matthiola) have been selected solely for the beauty of their flowers, but
the seeds differ greatly in colour and somewhat in size. Varieties of the
lettuce have been selected solely on account of their leaves, yet produce
seeds which likewise differ in colour. Generally, through the law of
correlation, when a variety differs greatly from its fellow-varieties in
any one character, it differs to a certain extent in several other
characters. I observed this fact when I cultivated together many varieties
of the same species, for I used first to make a list of the varieties which
differed most from each other in their foliage and manner of growth,
afterwards of those that differed most in their flowers, then in their
seed-capsules, and lastly in their mature seed; and I found that the same
names generally occurred in two, three, or four of the successive lists.
Nevertheless the greatest amount of difference between the varieties was
always exhibited, as far as I could judge, by that part or organ for which
the plant was cultivated.

When we bear in mind that each plant was at first cultivated because useful
to man, and that its variation was a subsequent, often a long subsequent,
event, we cannot explain the greater amount of diversity in the valuable
parts by supposing that species endowed with an especial tendency to vary