mature and shed, or is mechanically protruded, before the flower's own stigma is
ready; and such flowers absolutely require the presence of another hermaphrodite
for sexual union. But with the cowslip and various other species of Primula
there is this wide difference, that one individual, though it can fertilise
itself imperfectly, must unite with another individual for full fertility; it
cannot, however, unite with any other individual in the same manner as an
hermaphrodite plant can unite with any other one of the same species; or as one
snail or earth-worm can unite with any other hermaphrodite individual. On the
contrary, an individual belonging to one form of the cowslip in order to be
perfectly fertile must unite with one of the other form, just as a male
quadruped must and can unite only with the female.

I have spoken of the legitimate unions as being fully fertile; and I am fully
justified in doing so, for flowers artificially fertilised in this manner
yielded rather more seeds than plants naturally fertilised in a state of nature.
The excess may be attributed to the plants having been grown separately in good
soil. With respect to the illegitimate unions, we shall best appreciate their
degree of lessened fertility by the following facts. Gartner estimated the
sterility of the unions between distinct species, in a manner which allows of a
strict comparison with the results of the legitimate and illegitimate unions of
Primula. (1/6. 'Versuche uber die Bastarderzeugung' 1849 page 216.) With P.
veris, for every 100 seeds yielded by the two legitimate unions, only 64 were
yielded by an equal number of good capsules from the two illegitimate unions.
With P. Sinensis, as we shall hereafter see, the proportion was nearly the same-
-namely, as 100 to 62. Now Gartner has shown that, on the calculation of
Verbascum lychnitis yielding with its own pollen 100 seeds, it yielded when
fertilised by the pollen of Verbascum Phoeniceum 90 seeds; by the pollen of
Verbascum nigrum, 63 seeds; by that of Verbascum blattaria, 62 seeds. So again,
Dianthus barbatus fertilised by the pollen of D. superbus yielded 81 seeds, and
by the pollen of D. japonicus 66 seeds, relatively to the 100 seeds produced by