The plants in pots
were, however, exposed to less severe fluctuations of climate than those
out of doors; but their conditions, though closely uniform for all the
individuals of the same generation, differed somewhat in the successive
generations. Now, under these circumstances, the sexual elements of the
plants which were intercrossed in each generation retained sufficient
differentiation during several years for their offspring to be superior
to the self-fertilised, but this superiority gradually and manifestly
decreased, as was shown by the difference in the result between a cross
with one of the intercrossed plants and with a fresh stock. These
intercrossed plants tended also in a few cases to become somewhat more
uniform in some of their external characters than they were at first.
With respect to the plants which were self-fertilised in each
generation, their sexual elements apparently lost, after some years, all
differentiation, for a cross between them did no more good than a cross
between the flowers on the same plant. But it is a still more remarkable
fact, that although the seedlings of Mimulus, Ipomoea, Dianthus, and
Petunia which were first raised, varied excessively in the colour of
their flowers, their offspring, after being self-fertilised and grown
under uniform conditions for some generations, bore flowers almost as
uniform in tint as those on a natural species.
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