l apply to the varied
tints of the bark of trunks, branches, and twigs, which are often of
various shades of brown and green, or even vivid reds or yellows.

There are, however, a few cases in which the need of protection, which
we have found to be so important an agency in modifying the colours of
animals, has also determined those of some of the smaller members of the
vegetable kingdom. Dr. Burchell found a mesembryanthomum in South Africa
like a curiously shaped pebble, closely resembling the stones among
which it grew;[136] and Mr. J.P. Mansel Weale states that in the same
country one of the Asclepiadeae has tubers growing above ground among
stones which they exactly resemble, and that, when not in leaf, they are
for this reason quite invisible.[137] It is clear that such resemblances
must be highly useful to these plants, inhabiting an arid country
abounding in herbivorous mammalia, which, in times of drought or
scarcity, will devour everything in the shape of a fleshy stem or tuber.

True mimicry is very rare in plants, though adaptation to like
conditions often produces in foliage and habit a similarity that is
deceiving. Euphorbias growing in deserts often closely resemble cacti.
Seaside plants and high alpine plants of different orders are often much
alike; and innumerable resemblances of this kind are recorded in the
names of plants, as Veronica epacridea (the veronica like an epacris),
Limnanthemum nymphaeoides (the limnanthemum like a nymphaea), the
resembling species in each case belonging to totally distinct families.
But in these cases, and in most others that have been observed, the
essential features of true mimicry are absent, inasmuch as the one plant
cannot be supposed to derive any benefit from its close resemblance to
the other, and this is still more certain from the fact that the two
species usually inhabit different localities. A few cases exist,
however, in which there does seem to be the necessary accordance and
utility. Mr. Mansel Weale mentions a labiate plant (Ajuga ophrydis), the
only species of the genus Ajuga in South Africa, which is strikingly
like an orchid of the same country; while a balsam (Impatiens capensis),
also a solitary species of the genus in that country, is equally like an
orchid, growing in the same locality and visited by the same insects. As
both these genera of plants are specialised for insect fertilisation,
and both of the plants in question are isolated species of