If we suppose the process of deterioration of the male organs in
the mid-styled form to continue, the final result would be the production of a
female plant; and Lythrum salicaria would then consist of two heterostyled
hermaphrodites and a female. No such case is known to exist, but it is a
possible one, as hermaphrodite and female forms of the same species are by no
means rare. Although there is no reason to believe that heterostyled plants are
regularly becoming dioecious, yet they offer singular facilities, as will
hereafter be shown, for such conversion; and this appears occasionally to have
been effected.
We may feel sure that plants have been rendered heterostyled to ensure cross-
fertilisation, for we now know that a cross between the distinct individuals of
the same species is highly important for the vigour and fertility of the
offspring. The same end is gained by dichogamy or the maturation of the
reproductive elements of the same flower at different periods,--by
dioeciousness--self-sterility--the prepotency of pollen from another individual
over a plant's own pollen,--and lastly, by the structure of the flower in
relation to the visits of insects. The wonderful diversity of the means for
gaining the same end in this case, and in many others, depends on the nature of
all the previous changes through which the species has passed, and on the more
or less complete inheritance of the successive adaptations of each part to the
surrounding conditions.
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