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 similarly coloured flowers, than between those which
are differently coloured. Mr. Scott also has experimented on the species
and varieties of Verbascum; and although unable to confirm Gartner's
results on the crossing of the distinct species, he finds that the
dissimilarly coloured varieties of the same species yield fewer seeds,
in the proportion of eighty-six to 100, than the similarly coloured
varieties. Yet these varieties differ in no respect, except in the
colour of their flowers; and one variety can sometimes be raised from
the seed of another.

Kolreuter, whose accuracy has been confirmed by every subsequent
observer, has proved the remarkable fact that one particular variety
of the common tobacco was more fertile than the other varieties, when
crossed with a widely distinct species. He experimented 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 the 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 it can no longer be maintained that varieties when
crossed are invariably quite fertile. From the great difficulty of
ascertaining the infertility of varieties in a state of nature, for a
supposed variety, if proved to be infertile in any degree, would almost
universally be ranked as a species; from man attending only to external
characters in his domestic varieties, and from such varieties not having
been exposed for very long periods to uniform conditions of life; from
these several considerations we may conclude that fertility does not
constitute a fundamental distinction between varieties and species when
crossed. The general sterility of crossed species may safely be looked
at, not as a special acquirement or endowment, but as incidental on
changes of an unknown nature in their sexual elements.

HYBRIDS AND MONGRELS COMPARED, INDEPENDENTLY OF THEIR FERTILITY.

Independently of the question o