Their fertility ranges from zero to fertility
equalling that of the crossed flowers; and of this fact no explanation
can be offered. There are fifteen cases in the two tables in which the
number of seeds per capsule produced by the self-fertilised flowers
equals or even exceeds that yielded by the crossed flowers. Some few of
these cases are, I believe, accidental; that is, would not recur on a
second trial. This was apparently the case with the plants of the fifth
generation of Ipomoea, and in one of the experiments with Dianthus.
Nicotiana offers the most anomalous case of any, as the self-fertilised
flowers on the parent-plants, and on their descendants of the second and
third generations, produced more seeds than did the crossed flowers; but
we shall recur to this case when we treat of highly self-fertile
varieties.
It might have been expected that the difference in fertility between the
crossed and self-fertilised flowers would have been more strongly marked
in Table 9/G, in which the plants of one set were derived from
self-fertilised parents, than in Table 9/F, in which flowers on the
parent-plants were self-fertilised for the first time. But this is not
the case, as far as my scanty materials allow of any judgment. There is
therefore no evidence at present, that the fertility of plants goes on
diminishing in successive self-fertilised generations, although there is
some rather weak evidence that this does occur with respect to their
height or growth.
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