Thus, variations in the
caterpillar or the cocoon of the silkworm, in the eggs of poultry, and
in the seeds or young shoots of many culinary vegetables, have been
accumulated till those parts have become greatly modified and, for man's
purposes, improved. Owing to this fact it is easy for organisms to
become so modified as to avoid dangers that occur at any one period of
life. Thus it is that so many seeds have become adapted to various modes
of dissemination or protection. Some are winged, or have down or hairs
attached to them, so as to enable them to be carried long distances in
the air; others have curious hooks and prickles, which cause them to be
attached firmly to the fur of mammals or the feathers of birds; while
others are buried within sweet or juicy and brightly coloured fruits,
which are seen and devoured by birds, the hard smooth seeds passing
through their bodies in a fit state for germination. In the struggle for
existence it must benefit a plant to have increased means of dispersing
its seeds, and of thus having young plants produced in a greater variety
of soils, aspects, and surroundings, with a greater chance of some of
them escaping their numerous enemies and arriving at maturity.
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