hen visited by the proper
insects.

It must also be admitted that some few natural species appear under our
present state of knowledge to be perpetually self-fertilised, as in the
case of the Bee Ophrys (_O. apifera_), though adapted in its structure to
be occasionally crossed. The _Leersia oryzoides_ produces minute enclosed
flowers which cannot possibly be crossed, and these alone, to the exclusion
of the ordinary flowers, have as yet been known to yield seed.[195] A few
additional and analogous cases could be advanced. But these facts do not
make me doubt that it is a general law of nature that the individuals of
the same species occasionally intercross, and that some great advantage is
derived from this act. It is well known (and I shall hereafter have to give
instances) that some plants, both indigenous and naturalised, rarely or
never produce flowers; or, if they flower, never produce seeds. But no one
is thus led to doubt that it is a general law of nature that phanerogamic
plants should produce flowers, and that these flowers should produce seed.
When they fail, we believe that such plants would perform their proper
functions under different conditions, or that they formerly did so and will
do so again. On analogous grounds, I believe that the few flowers {92}
which do not now intercross, either would do so under different conditions,
or that they formerly fertilised each other at intervals--the means for
effecting this being generally still retained--and they will do so again at
some future period, unless indeed they become extinct. On this view alone,
many points in the structure and action of the reproductive organs in
hermaphrodite plants and animals are intelligible,--for instance, the male
and female organs never being so completely enclosed as to render access
from without impossible. Hence we may conclude that the most important of
all the means for giving uniformity to the individuals of the same species,
namely, the capacity of occasionally intercrossing, is present, or has been
formerly present, with all organic beings.

_On certain Characters not blending._--When two breeds are crossed
their characters usually become intimately fused together; but some
characters refuse to blend, and are transmitted in an unmodified state
either from both parents or from one. When grey and white mice are
paired, the young are not piebald nor of an intermediate tint, but are
pure white or of th