IN THE SPECIES OF PRIMULA. 91 
differing in their sexual powers and related to each other like males 
and females. There are many hermaphrodite animals which can- 
not fertilize themselves, but must unite with another hermaphro- 
dite: so it is with numerous plants ; for the pollen is often mature 
and shed, or is mechanically protruded, before the flower's own 
stigma is ready ; so that these hermaphrodite flowers absolutely 
require for their sexual union the presence of another hermaphro- 
dite. But in Primula there is this wide difference, that one indi- 
vidual Cowslip, for instance, though it can with mechanical aid im- 
perfectly fertilize itself, for full fertility must unite with another 
individual; but it cannot unite with any individual in the same 
manner as an hermaphrodite Snail or Earth-worm can unite with 
any other one Snail or Earth-worm ; but one form of the Cowslip, 
to be perfectly fertile, must unite with one of the other form, just 
as a male quadruped must and can unite only with a female. 
I have spoken of the heteromorphic union in Primula as result- 
ing in full fertility ; and I am fully justified, for the Cowslips thus 
fertilized actually gave rather more seed than the truly wild plants 
—a result which may be attributed to their good treatment and 
having grown separately. With respect to the lessened fertility 
of the homomorphie unions, we shall appreciate its degree best by 
the following facts. Gärtner has estimated the degree of sterility 
of the union of several distinct species *, in a manner which allows 
of the strictest comparison with the result of the heteromorphic 
and homomorphic unions of Primula. With P.veris, for every hun- 
dred seeds yielded by the heteromorphic unions, only sixty-four seeds 
were yielded by an equal number of good capsules from the homo- 
morphic unions. With P. Sinensis the proportion was nearly the 
same—namely, as 100 to 62. Now Gártner has shown that, on the 
calculation of Verbascum lychnitis yielding with its own pollen 
100 seeds, it yields when fertilized by the pollen of V. Pheeniceum 
ninety seeds; by the pollen of V. nigrum, sixty-three seeds; by 
that of V. blattaria, sixty-two seeds. So again, Dianthus barbatus 
fertilized by the pollen of D. superbus yielded eighty-one seeds, 
and by the pollen of D. Japonicus sixty-six seeds, relatively to 
the 100 seeds produced by its own pollen. Thus we see—and the 
fact is highly remarkable—that the homomorphic unions relatively 
to the heteromorphie unions in Primula are more sterile than the 
crosses between several distinct species relatively to the pure union 
of those species. 
The meaning or use of the existence in Primula of the two 
* Versuche über die Bastarderzeugung, 1849, s. 216. 
