The constitutional superiority of the crossed over the self-fertilised
plants was proved in another way in the third generation of Mimulus, by
self-fertilised seeds being sown on one side of a pot, and after a
certain interval of time crossed seeds on the opposite side. The
self-fertilised seedlings thus had (for I ascertained that the seeds
germinated simultaneously) a clear advantage over the crossed in the
start for the race. Nevertheless they were easily beaten (as may be seen
under the head of Mimulus) when the crossed seeds were sown two whole
days after the self-fertilised. But when the interval was four days, the
two lots were nearly equal throughout life. Even in this latter case the
crossed plants still possessed an inherent advantage, for after both
lots had grown to their full height they were cut down, and without
being disturbed were transferred to a larger pot, and when in the
ensuing year they had again grown to their full height they were
measured; and now the tallest crossed plants were to the tallest
self-fertilised plants in height as 100 to 75, and in fertility (i.e.,
by weight of seeds produced by an equal number of capsules from both
lots) as 100 to 34.
My usual method of proceeding, namely, to plant several pairs of crossed
and self-fertilised seeds in an equal state of germination on the
opposite sides of the same pots, so that the plants were subjected to
moderately severe mutual competition, was I think the best that could
have been followed, and was a fair test of what occurs in a state of
nature.
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