This view of the necessity of a large stock
of the same species for its preservation, explains, I believe, some
singular facts in nature such as that of very rare plants being sometimes
extremely abundant, in the few spots where they do exist; and that of some
social plants being social, that is abounding in individuals, even on the
extreme verge of their range. For in such cases, we may believe, that a
plant could exist only where the conditions of its life were so favourable
that many could exist together, and thus save the species from utter
destruction. I should add that the good effects of intercrossing, and the
ill effects of close interbreeding, no doubt come into play in many of
these cases; but I will not here enlarge on this subject.
COMPLEX RELATIONS OF ALL ANIMALS AND PLANTS TO EACH OTHER IN THE STRUGGLE
FOR EXISTENCE.
Many cases are on record showing how complex and unexpected are the checks
and relations between organic beings, which have to struggle together in
the same country. I will give only a single instance, which, though a
simple one, interested me. In Staffordshire, on the estate of a relation,
where I had ample means of investigation, there was a large and extremely
barren heath, which had never been touched by the hand of man; but several
hundred acres of exactly the same nature had been enclosed twenty-five
years previously and planted with Scotch fir.
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