This seems to me a remarkable physiological fact. The pollen-grains of the two
forms are undistinguishable under the microscope; the stigmas differ only in
length, degree of divergence, and in the size, shade of colour, and
approximation of their papillae, these latter differences being variable and
apparently due merely to the degree of elongation of the stigma. Yet we plainly
see that the two kinds of pollen and the two stigmas are widely dissimilar in
their mutual reaction--the stigmas of each form being almost powerless on their
own pollen, but causing, through some mysterious influence, apparently by simple
contact (for I could detect no viscid secretion), the pollen-grains of the
opposite form to protrude their tubes. It may be said that the two pollens and
the two stigmas mutually recognise each other by some means. Taking fertility as
the criterion of distinctness, it is no exaggeration to say that the pollen of
the long-styled Linum grandiflorum (and conversely that of the other form) has
been brought to a degree of differentiation, with respect to its action on the
stigma of the same form, corresponding with that existing between the pollen and
stigma of species belonging to distinct genera.
Linum perenne.
This species is conspicuously heterostyled, as has been noticed by several
authors.
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