Here, then, we have an enormous extension of the region of utility in
the vegetable kingdom, and one, moreover, which includes almost all the
specific characters of plants. For the species of plants are usually
characterised either by differences in the form, size, and colour of the
flowers, or of the fruits; or, by peculiarities in the shape, size,
dentation, or arrangement of the leaves; or by peculiarities in the
spines, hairs, or down with which various parts of the plant are
clothed. In the case of plants it must certainly be admitted that
"specific" characters are pre-eminently adaptive; and though there may
be some which are not so, yet all those referred to by Darwin as having
been adduced by various botanists as useless, either pertain to genera
or higher groups, or are found in some plants of a species only--that
is, are individual variations not specific characters.
In the case of animals, the most recent wide extension of the sphere of
utility has been in the matter of their colours and markings. It was of
course always known that certain creatures gained protection by their
resemblance to their normal surroundings, as in the case of white arctic
animals, the yellow or brown tints of those living in deserts, and the
green hues of many birds and insects surrounded by tropical vegetation.
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