; but some few cases both of
hybrids and mongrels long retaining uniformity of character could be given.
The variability, however, in the successive generations of mongrels is,
perhaps, greater than in hybrids.

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 superadded 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 {274} hybrids: Gaertner
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. Gaertner 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 Koelreuter.

These alone are the unimportant differences, which Gaertner 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 f