But it is of no use
considering this case and other analogous ones, for, as stated in the
Introduction, the coexistence of male and hermaphrodite plants is excessively
rare.
It is no valid objection to the foregoing views that changes of such a nature
would be effected with extreme slowness, for we shall presently see good reason
to believe that various hermaphrodite plants have become or are becoming
dioecious by many and excessively small steps. In the case of polygamous
species, which exist as males, females and hermaphrodites, the latter would have
to be supplanted before the species could become strictly dioecious; but the
extinction of the hermaphrodite form would probably not be difficult, as a
complete separation of the sexes appears often to be in some way beneficial. The
males and females would also have to be equalised in number, or produced in some
fitting proportion for the effectual fertilisation of the females.
There are, no doubt, many unknown laws which govern the suppression of the male
or female organs in hermaphrodite plants, quite independently of any tendency in
them to become monoecious, dioecious, or polygamous. We see this in those
hermaphrodites which from the rudiments still present manifestly once possessed
more stamens or pistils than they now do,--even twice as many, as a whole
verticil has often been suppressed.
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