EAST: INTERCROSSES BETWEEN SELF-STERILE PLANTS 143 



very last of the flowering season^ self-sterile plants may sometimes 

 become somewhat self-fertile. 



Darwin's (1876, p. 346) general conclusions are as follows: 



"Finally, the most interesting point in regard to self-sterile plants 

 is the evidence which they afford of the advantage, or rather the 

 necessity, of some degree or kind of differentiation in the sexual 

 elements, in order that they should unite and give birth to a new being. 

 It was ascertained that the five plants of Reseda odorata which were 

 selected by chance could be perfectly fertilised by pollen taken from 

 any one of them, but not by their own pollen; and a few additional 

 trials were made with some other individuals, which I have not 

 thought worth recording. So again, Hildebrand and Fritz Miiller 

 frequently speak of self-sterile plants being fertile with the pollen of 

 any other individual; and if there had been any exception to the 

 rule, these could hardly have escaped their observation and my own. 

 We may therefore confidently assert that a self-sterile plant can be 

 fertilised by the pollen of any one out of a thousand or ten thousand 

 individuals of the same species, but not by its own. Now it is obvi- 

 ously impossible that the sexual organs and elements of every indi- 

 vidual can have been specialised with respect to every other indi- 

 vidual. But there is no difficulty in believing that the sexual elements 

 of each differ slightly in the same diversified manner as do their 

 external characters; and it has often been remarked that no two 

 individuals are absolutely alike. Therefore we can hardly avoid the 

 conclusion that differences of an analogous and indefinite nature in 

 the reproductive system are sufficient to excite the mutual action of 

 the sexual elements, and that unless there be such differentiation 

 fertility fails." 



One cannot but admire these inductions Darwin has so cleverly 

 drawn from such meager data, nevertheless one cannot accept them 

 today just as they stand. The reasons for this statement will be 

 seen more clearly when our own data have been presented, but a brief 

 can be submitted with only the support of the work known to Darwin. 



In the first place, the seemingly contradictory results that were 

 obtained in the experiments on Reseda odorata are not necessarily con- 

 fusing. As reported, self-sterile plants produced varying ratios of 

 self-sterile and self-fertile plants. Unfortunately, the progeny of the 

 self-fertile plants was not followed. lilt has becD,. the problem might 

 have been more easily solved, for^ in all prob.abilit\-, the daughter 

 plants would have been self-sterile. It is my own belief, however, 

 tTiat the answt r (an \)v read in the casual remarks dropped by Darwin 

 in the midst ol his caret ul descriptions, remarks to which he paid little 

 attention. Darwin found that both EschschoUzia California and 

 Abiitilon darwinii, though self-sterile in Brazil tended to become self- 

 fertile in England, — especially late in the fl owering season. Now 



^ Cf. Darwin's observation on AbuUlon darwintt. 

 11 



