Other Kinds of Hybridizing 163 
AVERAGE AVERAGE No. OF 
jimall 
The legitimate 
unions 75 56 96.39 71.89 
The illegitimate 
unions 146 36 44.72 II.03 
The fertility of the legitimate to the illegitimate was found to 
be as 100 to 33, judged by the flowers that produced capsules, 
and as 100 to 46, as judged by the average number of seeds. 
Darwin concluded that only the pollen from the longest stamens 
can fully fertilize the longest pistil; only pollen jrom the mid- 
length stamens can fully fertilize the mid-length pistil, and only 
the shortest stamens can fully fertilize the shortest pistils. The 
meaning of this difference is entirely obscure. It is of much 
interest to find a condition of this sort between individuals of 
the same species. It suggests a comparison with the infertility 
that exists between different species; but in point of fact the 
results are just the reverse, for, in the present case, it is the same 
kind of flowers that imperfectly fertilize each other, while the 
flowers having a different form are more fertile. 
In the case of dimorphic or trimorphic plants Darwin makes 
a determined effort to show that selection of fluctuating variations 
has brought about the two kinds of flowers. This argument is 
so instructive that I shall give it in full. 
Since heterostyled plants occur in fourteen different families 
of plants, it is probable, Darwin thinks, that this condition has 
been acquired independently in each family and “that it can be 
acquired without any great difficulty.” The first step in the pro- 
cess he imagines to have been due to great variability in the 
length of the pistil and stamens. ‘As most plants are occasion- 
ally cross-fertilized by the aid of insects, we may assume that 
this was the case with our supposed varying plant but that it 
would have been beneficial to it to have been more regularly 
cross-fertilized.” ‘This would have been better accomplished 
if the stigma and the stamens stood at the same line; but as the 
