(6/6. Gartner 'Bastarderzeugung im
Pflanzenreich' 1849 page 165.) But what the nature of the inner constitutional
differences may be between the sets or forms of the same varying species, or
between distinct species, is quite unknown. It seems therefore probable that the
species which have become heterostyled at first varied so that two or three sets
of individuals were formed differing in the length of their pistils and stamens
and in other co-adapted characters, and that almost simultaneously their
reproductive powers became modified in such a manner that the sexual elements in
one set were adapted to act on the sexual elements of another set; and
consequently that these elements in the same set or form incidentally became
ill-adapted for mutual interaction, as in the case of distinct species. I have
elsewhere shown that the sterility of species when first crossed and of their
hybrid offspring must also be looked at as merely an incidental result,
following from the special co-adaptation of the sexual elements of the same
species. (6/7. 'Origin of Species' 6th edition page 247; 'Variation of Animals
and Plants under Domestication' 2nd edition volume 2 page 169; 'The Effects of
Cross and Self-fertilisation' page 463. It may be well here to remark that,
judging from the remarkable power with which abruptly changed conditions of life
act on the reproductive system of most organisms, it is probable that the close
adaptation of the male to the female elements in the two forms of the same
heterostyled species, or in all the individuals of the same ordinary species,
could be acquired only under long-continued nearly uniform conditions of life.
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