In regard to the sterility of hybrids in successive generations; though
Gartner was enabled to rear some hybrids, carefully guarding them from
a cross with either pure parent, for six or seven, and in one case for
ten generations, yet he asserts positively that their fertility never
increased, but generally greatly decreased. I do not doubt that this is
usually the case, and that the fertility often suddenly decreases in
the first few generations. Nevertheless I believe that in all these
experiments the fertility has been diminished by an independent cause,
namely, from close interbreeding. I have collected so large a body of
facts, showing
that close interbreeding lessens fertility, and, on the other hand,
that an occasional cross with a distinct individual or variety
increases fertility, that I cannot doubt 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 season: hence
hybrids will generally be fertilised during each generation by their
own individual pollen; and I am convinced that this would be injurious
to their fertility, already lessened by their hybrid origin. I am
strengthened in this conviction by a remarkable statement repeatedly
made by Gartner, namely, that if even the less fertile hybrids be
artificially fertilised with hybrid pollen of the same kind, their
fertility, notwithstanding the frequent ill effects of manipulation,
sometimes decidedly increases, and goes on increasing. Now, in
artificial fertilisation 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 on the same plant, would be thus
effected. Moreover, whenever complicated experiments are in progress,
so careful an observer as Gartner would have castrated his hybrids, and
this would have insured in each generation a cross with the 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 the increase of
fertility in the successive generations of _artificially fertilised_
hybrids may, I believe, be accounted for by close interbreeding having
been avoided.
Now let us turn to the results arrived at by the third most experienced
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