d fertilised by insects; while the more complex
modes, existing for the most part in the highly irregular flowers, may
result from those cases in which adaptation to insect-fertilisation, and
partial or complete degradation to self-fertilisation or to
wind-fertilisation, have again and again recurred, each time producing
some additional complexity, arising from the working up of old rudiments
for new purposes, till there have been reached the marvellous flower
structures of the papilionaceous tribes, of the asclepiads, or of the
orchids.

We thus see that the existing diversity of colour and of structure in
flowers is probably the ultimate result of the ever-recurring struggle
for existence, combined with the ever-changing relations between the
vegetable and animal kingdoms during countless ages. The constant
variability of every part and organ, with the enormous powers of
increase possessed by plants, have enabled them to become again and
again readjusted to each change of condition as it occurred, resulting
in that endless variety, that marvellous complexity, and that exquisite
colouring which excite our admiration in the realm of flowers, and
constitute them the perennial charm and crowning glory of nature.

_Flowers the Product of Insect Agency._

In his _Origin of Species_, Mr. Darwin first stated that flowers had
been rendered conspicuous and beautiful in order to attract insects,
adding: "Hence we may conclude that, if insects had not been developed
on the earth, our plants would not have been decked with beautiful
flowers, but would have produced only such poor flowers as we see on our
fir, oak, nut, and ash trees, on grasses, docks, and nettles, which are
all fertilised through the agency of the wind." The argument in favour
of this view is now much stronger than when he wrote; for not only have
we reason to believe that most of these wind-fertilised flowers are
degraded forms of flowers which have once been insect fertilised, but we
have abundant evidence that whenever insect agency becomes comparatively
ineffective, the colours of the flowers become less bright, their size
and beauty diminish, till they are reduced to such small, greenish,
inconspicuous flowers as those of the rupture-wort (Herniaria glabra),
the knotgrass (Polygonum aviculare), or the cleistogamic flowers of the
violet. There is good reason to believe, therefore, not only that
flowers have been developed in order to attract insects to ai