But this conclusion is
directly opposed by some other cases, for instance by that of Linum
grandiflorum; for here the long-styled form is utterly barren with its own-form
pollen, although from the position of the anthers this pollen is invariably
applied to the stigma. It is obvious that with heterostyled dimorphic plants the
two female and the two male organs differ in power; for if the same kind of
pollen be placed on the stigmas of the two forms, and again if the two kinds of
pollen be placed on the stigmas of the same form, the results are in each case
widely different. Nor can we see how this differentiation of the two female and
two male organs could have been effected merely through each kind of pollen
being habitually placed on one of the two stigmas.
Another view seems at first sight probable, namely, that an incapacity to be
fertilised in certain ways has been specially acquired by heterostyled plants.
We may suppose that our varying species was somewhat sterile (as is often the
case) with pollen from its own stamens, whether these were long or short; and
that such sterility was transferred to all the individuals with pistils and
stamens of the same length, so that these became incapable of intercrossing
freely; but that such sterility was eliminated in the case of the individuals
which differed in the length of their pistils and stamens.
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