The seeds sown at the same time in a garden have
generally been matured during the same season and in the same place; and
in this respect they differ much from the seeds sown by the hand of
nature. Some exotic plants are not frequented by the native insects in
their new home, and therefore are not intercrossed; and this appears to
be a highly important factor in the individuals acquiring uniformity of
constitution.
In my experiments the greatest care was taken that in each generation
all the crossed and self-fertilised plants should be subjected to the
same conditions. Not that the conditions were absolutely the same, for
the more vigorous individuals will have robbed the weaker ones of
nutriment, and likewise of water when the soil in the pots was becoming
dry; and both lots at one end of the pot will have received a little
more light than those at the other end. In the successive generations,
the plants were subjected to somewhat different conditions, for the
seasons necessarily varied, and they were sometimes raised at different
periods of the year. But as they were all kept under glass, they were
exposed to far less abrupt and great changes of temperature and moisture
than are plants growing out of doors. With respect to the intercrossed
plants, their first parents, which were not related, would almost
certainly have differed somewhat in constitution; and such
constitutional peculiarities would be variously mingled in each
succeeding intercrossed generation, being sometimes augmented, but more
commonly neutralised in a greater or less degree, and sometimes revived
through reversion; just as we know to be the case with the external
characters of crossed species and varieties.
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