REPRODUCTIVE ORGANS IN THE PRIMULACER. 125 
remarkable sexual characteristics of the correlated species, and 
thus presenting an illustration of incipient dimorphism. 
The usual differences in the fertility of the heteromorphie and 
homomorphie unions will be best appreciated by giving the mean 
results from the unions of several species. Thus, taking the five 
heteromorphic and homomorphie unions given above, namely, 
P. Auricula, Sikkimensis, cortusoides, involucrata, and farinosa, 
we see, from the mean results of their combined produets, that for 
every 100 seeds yielded by the heteromorphie unions, only twenty- 
four are yielded by the homomorphic unions,—the heteromorphie 
thus exceeding the homomorphie unions in about the proportion 
of five to three! I have also shown the remarkable fact that the 
pollen of a distinct species will produce a much higher grade of 
fertility than an ordinary homomorphic union, i.e. a flower's own 
pollen ! 
Itis well known that A will fertilize B, and B will not fertilize A. 
I have given instances of this law with Primulas. I have also 
shown the new and remarkable fact, that of the two forms of the 
same species the pollen of the one, but not of the other, will fertilize 
a distinct species! For example, the long-styled P. Pallinurii 
can be fertilized readily by pollen of the long-styled P. Auricula ; 
yet, after numerous trials, I have failed to effect a single union 
between the long-styled form of the P. Pallinurii and the short- 
styled P. Auricula. How utterly inconsistent, then, are such facts 
with the teachings of those who would have us believe that an 
absolute causal relation exists between the sterility from hybridism 
and systematic affinity! On the other hand, how unequivocally do 
these cases show us that the greater or less facility of one species 
to unite with another is, as Mr. Darwin has sagaciously argued, 
“incidental on inappreciable differences in their reproductive 
systems. And that there is no more reason to think that species 
have been specially endowed with various degrees of sterility to 
prevent them crossing and blending in nature, than to think that 
trees have been specially endowed with various and somewhat 
analogous degrees of difficulty in being grafted together in order 
to prevent them becoming inarched in our forests." * 
Probably the most remarkable result from my observations is 
that when the dimorphic species cease to be dimorphie, their 
reproductive functions are greatly modified. Thus, in the case of 
the Cowslip, for example, we have seen that an ordinary homo- 
morphic union yields about fourteen seeds per capsule, the hetero- 
* «Origin of Species,’ 3rd edit. p. 299. 
