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.

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.