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independent cause, namely,
close interbreeding. I have
so
→large a body of
facts, showing
→OMIT
on the
that an occasional cross with a distinct individual or variety increases
→the vigour and fertility of the offspring, and on the other hand that very close interbreeding lessens their vigour and fertility,
that I
the correctness of this
→almost universal belief amongst breeders. Hybrids are seldom raised by experimentalists in great numbers; and as the parent-species, or other allied hybrids, generally grow in the same garden, the visits of insects must be carefully prevented during the flowering
hence
→will
generally
→have to be
fertilised during each generation by
→their own individual pollen; and
this would
injurious to their fertility, already lessened by their hybrid origin. I am strengthened in this conviction by a remarkable statement repeatedly made by Gärtner, namely, that if even the less fertile hybrids be artificially
with hybrid pollen of the same kind, their fertility, notwithstanding the frequent ill effects
manipulation, sometimes decidedly increases, and goes on increasing. Now, in
→the process of artificial
pollen is as often taken by chance (as I know from my own experience) from the anthers of another flower, as from the anthers of the flower itself which is to be fertilised; so that a cross between two flowers, though probably
the same plant, would be thus effected. Moreover, whenever complicated experiments are in progress, so careful an observer as Gärtner would have castrated his hybrids, and this would have
in each generation a cross with
pollen from a distinct flower, either from the same plant or from another plant of the same hybrid nature. And thus, the strange fact of
increase of fertility in the successive generations of
artificially
fertilised
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