28O D. F. JONES. 



tion to its solution and give a complete resume of the work 

 which has been done on this subject. They have been able to 

 demonstrate that groups exist within which the individuals are 

 all both self-sterile and cross-sterile, but any member of one 

 group is perfectly fertile with any member of any other group. 

 These investigators find that there are about 100 well-endorsed 

 instances of self-sterility in plants scattered over some 35 families. 

 Undoubtedly this discrimination is a means to promote cross- 

 fertilization of approximately the same significance as floral 

 contrivances, dichogamy and dioecism. Even though widespread 

 in its occurrence self-sterility is a special adaptive process ful- 

 filling a particular function. It is directly opposite in its effect 

 to the results found in maize which shows no self-sterility of the 

 type found in Nicotiana and other genera. At least no clear cases 

 are known of maize pollen, which is unable to fertilize the plants 

 which produced it, being able to fertilize other plants. 



Darwin has furnished many instances of self-sterility. In 

 addition he reports some experiments which led him to believe 

 that even when a plant was normally self-fertile that pollen 

 from unrelated plants of the same species was prepotent over 

 the plant's own pollen. In discussing means which insure flowers 

 being fertilized with pollen from distinct plants, he says: "We 

 now come to a far more general and therefore more important 

 means by which the mutual fertilization of distinct plants is 

 effected, namely, the fertilizing power of pollen from another 

 variety or individual being greater than that of a plant's own 

 pollen. The simplest and best know T n case of prepotent action 

 in pollen, though it does not bear directly on our present subject ( 

 is that of a plant's own pollen over that from a distinct species. 

 If pollen from a distinct species be placed on the stigma of a 

 castrated flower, and then after the interval of several hours, 

 pollen from the same species be placed on the stigma, the effects 

 of the former are wholly obliterated, excepting in some rare cases. 

 If tw r o varieties are treated in the same manner, the result is 

 analogous, though of directly opposite nature; for pollen from 

 any other variety is often or generally prepotent over that from 

 the same flower" ("Cross- and Self-Fertilization, " pp. 391-392). 



These statements were based on observations and experiments 



