ilisation--Fertilisation of flowers by
birds--Self-fertilisation of flowers--Difficulties and
contradictions--Intercrossing not necessarily
advantageous--Supposed evil results of close interbreeding--How
the struggle for existence acts among flowers--Flowers the
product of insect agency--Concluding remarks on colour in
nature.

The colours of plants are both less definite and less complex than are
those of animals, and their interpretation on the principle of utility
is, on the whole, more direct and more easy. Yet here, too, we find that
in our investigation of the uses of the various colours of fruits and
flowers, we are introduced to some of the most obscure recesses of
nature's workshop, and are confronted with problems of the deepest
interest and of the utmost complexity.

So much has been written on this interesting subject since Mr. Darwin
first called attention to it, and its main facts have become so
generally known by means of lectures, articles, and popular books, that
I shall give here a mere outline sketch, for the purpose of leading up
to a discussion of some of the more fundamental problems which arise out
of the facts, and which have hitherto received less attention than they
deserve.

_The General Colour Relations of Plants._

The green colour of the foliage of leafy plants is due to the existence
of a substance called chlorophyll, which is almost universally developed
in the leaves under the action of light. It is subject to definite
chemical changes during the processes of growth and of decay, and it is
owing to these changes that we have the delicate tints of spring
foliage, and the more varied, intense, and gorgeous hues of autumn. But
these all belong to the class of intrinsic or normal colours, due to the
chemical constitution of the organism; as colours they are unadaptive,
and appear to have no more relation to the wellbeing of the plants
themselves than have the colours of gems and minerals. We may also
include in the same category those algae and fungi which have bright
colours--the "red snow" of the arctic regions, the red, green, or purple
seaweeds, the brilliant scarlet, yellow, white, or black agarics, and
other fungi. All these colours are probably the direct results of
chemical composition or molecular structure, and, being thus normal
products of the vegetable organism, need no special explanation from our
present point of view; and the same remark wil