This greater variability of mongrels than of hybrids does not seem to
me at all surprising. For the parents of mongrels are varieties, and
mostly domestic varieties (very few experiments having been tried on
natural varieties), and this implies in most cases that there has been
recent variability; and therefore we might expect that such variability
would often continue and be super-added to that arising from the mere
act of crossing. 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.
These alone are the unimportant differences, which Gartner is able to
point out, between hybrid and mongrel plants. On the other hand, the
resemblance in mongrels and in hybrids to their respective parents,
more especially in hybrids produced from nearly related species,
follows according to Gartner the same laws. When two species are
crossed, one has sometimes a prepotent power of impressing its likeness
on the hybrid; and so I believe it to be with varieties of plants. With
208