Other Kinds of Hybridizing 



163 



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 from 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 



