") As far
as anemophilous plants are concerned, we know that they are apt to have
their sexes separated, and we can see that it would be an unfavourable
circumstance for them to bear their flowers very close to the ground, as
their pollen is liable to be blown high up in the air (10/62. Kerner
'Schutzmittel des Pollens' 1873 page 4.); but as the culms of grasses
give sufficient elevation, we cannot thus account for so many trees and
bushes being diclinous. We may infer from our previous discussion that a
tree bearing numerous hermaphrodite flowers would rarely intercross with
another tree, except by means of the pollen of a distinct individual
being prepotent over the plants' own pollen. Now the separation of the
sexes, whether the plant were anemophilous are entomophilous, would most
effectually bar self-fertilisation, and this may be the cause of so many
trees and bushes being diclinous. Or to put the case in another way, a
plant would be better fitted for development into a tree, if the sexes
were separated, than if it were hermaphrodite; for in the former case
its numerous flowers would be less liable to continued
self-fertilisation. But it should also be observed that the long life of
a tree or bush permits of the separation of the sexes, with much less
risk of evil from impregnation occasionally failing and seeds not being
produced, than in the case of short-lived plants.
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