ber proportionally to the supply of seed, as their
numbers are checked during winter; but any one who has tried, knows how
troublesome it is to get seed from a few wheat or other such plants in a
garden: I have in this case lost every single seed. 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 favorable that many could exist together
and thus save the species from utter destruction. I should add that the
good effects of inter-crossing, and the ill effects of close
inter-breeding, no doubt come into play in many of these cases; but I
will not here enlarge on this subject.

THE COMPLEX RELATIONS OF ALL ANIMALS AND PLANTS TO EACH OTHER IN THE
STRUGGLE FOR EXISTENCE

From the 'Origin of Species'

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 inclosed
twenty-five years previously and planted with Scotch fir. The change in
the native vegetation of the planted part of the heath was most
remarkable, more than is generally seen in passing from one quite
different soil to another: not only the proportional numbers of the
heath-plants were wholly changed, but twelve species of plants (not
counting grasses and carices) flourished in the plantations, which could
not be found on the heath. The effect on the insects must have been
still greater, for six insectivorous birds were very common in the
plantations which were not to be seen on the heath; and the heath was
frequented by two or three distinct insectivorous birds. Here we see how
potent has been the effect of the introduction of a single tree, nothing
whatever else having been done, with the exception of the land having