This holds good especially in cold and temperate
regions, where insects are not so numerous as under a warmer climate,
and where consequently entomophilous plants are less favourably
situated. We see this in our forests of Coniferae and other trees, such
as oaks, beeches, birches, ashes, etc.; and in the Gramineae,
Cyperaceae, and Juncaceae, which clothe our meadows and swamps; all
these trees and plants being fertilised by the wind. As a large quantity
of pollen is wasted by anemophilous plants, it is surprising that so
many vigorous species of this kind abounding with individuals should
still exist in any part of the world; for if they had been rendered
entomophilous, their pollen would have been transported by the aid of
the senses and appetites of insects with incomparably greater safety
than by the wind. That such a conversion is possible can hardly be
doubted, from the remarks lately made on the existence of intermediate
forms; and apparently it has been effected in the group of willows, as
we may infer from the nature of their nearest allies. (10/55. Hermann
Muller 'Die Befruchtung' etc. page 149.)
It seems at first sight a still more surprising fact that plants, after
having been once rendered entomophilous, should ever again have become
anemophilous; but this has occasionally though rarely occurred, for
instance, with the common Poterium sanguisorba, as may be inferred from
its belonging to the Rosaceae.
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