[4] Even a plant like the potato--so widely cultivated, so
hardy, and so well adapted to spread by means of its many-eyed
tubers--has not established itself in a wild state in any part of
Europe. It would be thought that Australian plants would easily run
wild in New Zealand. But Sir Joseph Hooker informs us that the late Mr.
Bidwell habitually scattered Australian seeds during his extensive
travels in New Zealand, yet only two or three Australian plants appear
to have established themselves in that country, and these only in
cultivated or newly moved soil.
These few illustrations sufficiently show that all the plants of a
country are, as De Candolle says, at war with each other, each one
struggling to occupy ground at the expense of its neighbour. But,
besides this direct competition, there is one not less powerful arising
from the exposure of almost all plants to destruction by animals. The
buds are destroyed by birds, the leaves by caterpillars, the seeds by
weevils; some insects bore into the trunk, others burrow in the twigs
and leaves; slugs devour the young seedlings and the tender shoots,
wire-worms gnaw the roots.
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