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Darwin, Charles, 1809-1882

"The Different Forms of Flowers on Plants of the Same Species"

(2/18. 'Journal of the Linnean Society Botany' volume 8 1864
page 93 to end.) I have already alluded to his statement, that in four instances
(not to mention others) a species when crossed with a distinct one yielded a
larger number of seeds than the same species fertilised illegitimately with its
own-form pollen, though taken from a distinct plant. It has long been known from
the researches of Kolreuter and Gartner, that two species when crossed
reciprocally sometimes differ as widely as is possible in their fertility: thus
A when crossed with the pollen of B will yield a large number of seeds, whilst B
may be crossed repeatedly with pollen of A, and will never yield a single seed.
Now Mr. Scott shows in several cases that the same law holds good when two
heterostyled species of Primula are intercrossed, or when one is crossed with a
homostyled species. But the results are much more complicated than with ordinary
plants, as two heterostyled dimorphic species can be intercrossed in eight
different ways. I will give one instance from Mr. Scott. The long-styled P.
hirsuta fertilised legitimately and illegitimately with pollen from the two
forms of P. auricula, and reciprocally the long-styled P. auricula fertilised
legitimately and illegitimately with pollen from the two forms of P. hirsuta,
did not produce a single seed.


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