cies of Verbascum when intercrossed
produce less seed, than do either coloured varieties when fertilised
with pollen from their own coloured flowers. Moreover, he asserts that
when yellow and white varieties of one species are crossed with yellow
and white varieties of a DISTINCT species, more seed is produced by the
crosses between the same coloured flowers, than between those which are
differently coloured. Yet these varieties of Verbascum present no other
difference besides the mere colour of the flower; and one variety can
sometimes be raised from the seed of the other.

From observations which I have made on certain varieties of hollyhock, I
am inclined to suspect that they present analogous facts.

Kolreuter, whose accuracy has been confirmed by every subsequent
observer, has proved the remarkable fact, that one variety of the common
tobacco is more fertile, when crossed with a widely distinct species,
than are the other varieties. He experimentised on five forms, which are
commonly reputed to be varieties, and which he tested by the severest
trial, namely, by reciprocal crosses, and he found their mongrel
offspring perfectly fertile. But one of these five varieties, when used
either as father or mother, and crossed with the Nicotiana glutinosa,
always yielded hybrids not so sterile as those which were produced
from the four other varieties when crossed with N. glutinosa. Hence the
reproductive system of this one variety must have been in some manner
and in some degree modified.

From these facts; from the great difficulty of ascertaining the
infertility of varieties in a state of nature, for a supposed variety if
infertile in any degree would generally be ranked as species; from
man selecting only external characters in the production of the most
distinct domestic varieties, and from not wishing or being able to
produce recondite and functional differences in the reproductive system;
from these several considerations and facts, I do not think that the
very general fertility of varieties can be proved to be of universal
occurrence, or to form a fundamental distinction between varieties
and species. The general fertility of varieties does not seem to me
sufficient to overthrow the view which I have taken with respect to
the very general, but not invariable, sterility of first crosses and of
hybrids, namely, that it is not a special endowment, but is incidental
on slowly acquired modifications, more especially in