5 seeds
per capsule. The primrose, especially the short-styled form, when fertilised by
the cowslip, is less sterile, as Gartner likewise observed, than is the cowslip
when fertilised by the primrose. The above experiments also show that a cross
between the same forms of the primrose and cowslip is much more sterile than
that between different forms of these two species.
The seeds from the several foregoing crosses were sown, but none germinated
except those from the short-styled primrose fertilised with pollen of the
polyanthus; and these seeds were the finest of the whole lot. I thus raised six
plants, and compared them with a group of wild oxlips which I had transplanted
into my garden. One of these wild oxlips produced slightly larger flowers than
the others, and this one was identical in every character (in foliage, flower-
peduncle, and flowers) with my six plants, excepting that the flowers of the
latter were tinged of a dingy red colour, from being descended from the
polyanthus.
We thus see that the cowslip and primrose cannot be crossed either way except
with considerable difficulty, that they differ conspicuously in external
appearance, that they differ in various physiological characters, that they
inhabit slightly different stations and range differently. Hence those botanists
who rank these plants as varieties ought to be able to prove that they are not
as well fixed in character as are most species; and the evidence in favour of
such instability of character appears at first sight very strong.
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