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 stamens, and
carry grains of the pollen to the next flower they visit.
We have here a very fertile line of development among the
primitive flowers. The insects begin to visit them, for their
pollen or juices, and cross-fertilise them. If this is an
advantage, attractiveness to insects will become so important a
feature that natural selection will develop it more and more. In
plain English, what is meant is that those flowers which are more
attractive to insects will be the most surely fertilised and
breed most, and the prolonged application of this principle
during hundreds of thousands of years will issue in the immense
variety of our flowers. They will be enriched with little stores
of honey and nectar; not so mysterious an advantage, when we
reflect on the concentration of the juices in the neighbourhood
of the seed.
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