Self-Sterility 137 



made to explain self-sterility as a response. It was 

 demonstrated that when a race of plants was grown 

 under conditions of unusually high humidity its pollen 

 grains would burst before they had a chance to function. 

 This explanation was obviously true in a few simple cases, 

 but the phenomenon of self-sterility usually involves 

 something much more perplexing than merely the non- 

 functioning of pollen. The real problem is to explain 

 why pollen will not function on "own" stigmas and 

 will function on the stigmas of other closely related races, 

 while it requires foreign pollen to function on "own" 

 stigmas. Such a complex situation could hardly be 

 explained as a response; more probably it is involved 

 with inheritance. Morphologists, cytologists, ecologists, 

 physiologists, and practical horticulturists have all 

 contributed explanations; in fact, it is not assured as yet 

 to which of these fields the phenomenon belongs. 

 In the meantime, what concerns us is whether self- 

 sterility can be explained by the principles of genetics. 



Such a theory has been proposed. Several investi- 

 gators have suggested that there is a heritable factor for 

 self-sterility, and some investigations of this possibility 

 have been undertaken, but as yet most of the results 

 have been negative. It must be realized, however, that 

 if self-sterility is ever to be explained on the basis of 

 hereditary factors the mechanism involved will be 

 rather unusual. Although most of the explanations 

 proposed by geneticists have proved inadequate there is 

 at least one that deserves consideration. It is a typical 

 Mendelian explanation and very ingenious. It fitted the 

 facts perfectly when first proposed and, still better, it 

 has continued to fit the facts that have been uncovered 



