It is therefore a most curious and suggestive fact, that in all the
recorded cases, in which a decided infertility occurs between varieties
of the same species, those varieties are distinguished by a difference
of colour. The infertile varieties of Verbascum were white and yellow
flowered respectively; the infertile varieties of maize were red and
yellow seeded; while the infertile pimpernels were the red and the blue
flowered varieties. So, the differently coloured varieties of
hollyhocks, though grown close together, each reproduce their own colour
from seed, showing that they are not capable of freely intercrossing.
Yet Mr. Darwin assures us that the agency of bees is necessary to carry
the pollen from one plant to another, because in each flower the pollen
is shed before the stigma is ready to receive it. We have here,
therefore, either almost complete sterility between varieties of
different colours, or a prepotent effect of pollen from a flower of the
same colour, bringing about the same result.
Similar phenomena have not been recorded among animals; but this is not
to be wondered at when we consider that most of our pure and valued
domestic breeds are characterised by definite colours which constitute
one of their distinctive marks, and they are, therefore, seldom crossed
with these of another colour; and even when they are so crossed, no
notice would be taken of any slight diminution of fertility, since this
is liable to occur from many causes.
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