The slight degree of variability in
hybrids from the first cross or in the first generation, in contrast
with their extreme variability in the succeeding generations, is a
curious fact and deserves attention. For it bears on and corroborates
the view which I have taken on the cause of ordinary variability;
namely, that it is due to the reproductive system being eminently
sensitive to any change in the conditions of life, being thus often
rendered either impotent or at least incapable of its proper function
of producing offspring identical with the parent-form. Now hybrids in
the first generation are descended from species (excluding those long
cultivated) which have not had their reproductive systems in any way
affected, and they are not variable; but hybrids themselves have their
reproductive systems seriously affected, and their descendants are
highly variable.
But to return to our comparison of mongrels and hybrids: Gartner
states that mongrels are more liable than hybrids to revert to either
parent-form; but this, if it be true, is certainly only a difference
in degree. Gartner further insists that when any two species, although
most closely allied to each other, are crossed with a third species,
the hybrids are widely different from each other; whereas if two very
distinct varieties of one species are crossed with another species,
the hybrids do not differ much. But this conclusion, as far as I can
make out, is founded on a single experiment; and seems directly
opposed to the results of several experiments made by Kolreuter.
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