DARWIN ON THE PRIMROSE xxvii 



discussion of a single case. Its consideration will also 

 serve to show the wide divergence between the true 

 bearing of the discovery itself and the claims of Men- 

 delians. 



' The thrum-eyed condition of the primrose has been 

 shown by Bateson and Gregory to be a Mendelian domi- 

 nant to the pin-eyed condition, so that we have here the 

 solution, so far as solution is possible, of a biological 

 problem to which Darwin devoted the greater part of a 

 volume.' 1 



Let us inquire what Darwin did achieve in the pages 

 referred to ; for Lock only leads his readers to infer that 

 the great naturalist failed to find a solution. 



i. In the first place, Darwin examined not only the 

 primrose, but all the heterostyled plants of which he 

 could obtain specimens, paying special attention to such 

 points as the diameter of the pollen-grains, the structure 

 of the stigma, &c. For he would by no means accept 

 differences in length of stamen and pistil alone as suffi- 

 cient evidence of the heterostyled condition. 



2. After proving that the plants were truly hetero- 

 styled, he showed in all available species, by numbers of 

 laborious experiments, that one form of a heterostyled 

 plant is only fully fertilized by pollen from an individual 

 of the other form (or one of the other forms in the case 

 of trimorphic heterostyled plants). 



3. He proved that when the stigma receives pollen 

 from a form the same as its own, together with pollen 

 from the other form, the latter is prepotent. 



4. As regards some of the species, he proved, by 

 covering with a net, that the visits of insects are necessary 



1 R. H. Lock, Variation, Heredity and Evolution, London, 1906, 

 p. 201. Darwin's volume referred to is Different Forms of Flowers 

 (London, 1877). 



