For, where could the rich lowland _equatorial_ flora
have existed during a period of general refrigeration sufficient for
this? and what became of the wonderfully rich Cape flora which, if the
temperature of Tropical Africa had been so recently lowered, would
certainly have spread northwards and on the return of the heat could
hardly have been driven back into the sharply defined and _very
restricted area_ in which it now exists?
As to the migration of plants from mountain to mountain not being so
probable as to remote islands, I think that is fully counterbalanced by
two considerations:
(a) The area and abundance of the mountain stations along such a range
as the Andes are immensely greater than those of the islands in the
North Atlantic, for example.
(b) The temporary occupation of mountain stations by migrating plants
(which I think I have shown to be probable) renders _time_ a much more
important element in increasing the number and variety of the plants so
dispersed than in the case of islands, where the flora soon acquires a
fixed and endemic character, and where the number of species is
necessarily limited.
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