are generally white or
pink; the most advanced flowers of all families, and almost all the
flowers of the more advanced families, are red, purple, or blue; and the
most advanced flowers of the most advanced families are always
either blue or variegated. Professor Henslow adds a number of equally
significant facts with the same tendency, so that we have strong reason
to conceive the floral world as passing through successive phases of
colour in the Tertiary Era. At first it would be a world of yellows
and greens, like that of the Mesozoic vegetation, but brighter. In time
splashes of red and white would lie on the face of the landscape; and
later would come the purples, the rich blues, and the variegated colours
of the more advanced flowers.

Why the colours came at all is a question closely connected with the
general story of the evolution of the flower, at which we must glance.
The essential characteristic of the flower, in the botanist's judgment,
is the central green organ which you find--say, in a lily--standing out
in the middle of the floral structure, with a number of yellow-coated
rods round it. The yellow rods bear the male germinal elements (pollen);
the central pistil encloses the ovules, or female elements. "Angiosperm"
means "covered-seed plant," and its characteristic is this protection
of the ovules within a special chamber, to which the pollen alone may
penetrate. Round these essential organs are the coloured petals of the
corolla (the chief part of the flower to the unscientific mind) and the
sepals, often also coloured, of the calyx.

There is no doubt that all these parts arose from modifications of the
leaves or stems of the primitive plant; though whether the bright
leaves of the corolla are directly derived from ordinary leaves, or are
enlarged and flattened stamens, has been disputed. And to the question
why these bright petals, whose colour and variety of form lend such
charm to the world of flowers, have been developed at all, most
botanists will give a prompt and very interesting reply. As both male
and female elements are usually in one flower, it may fertilise itself,
the pollen falling directly on the pistil. But fertilisation is more
sure and effective if the pollen comes from a different individual--if
there is "cross fertilisation." This may be accomplished by the simple
agency of the wind blowing the pollen broadcast, but it is done much
better by insects, which brush against the stame