Self-Sterility 141 



and brings abnormal results. Therefore the gameto- 

 phyte having the abnormal double dose (XY) is just as 

 sterile as the gametophyte with no dose (OO). 



In developing the F 2 ratios of course only the fertile 

 gametophytes function. XY and OO are eliminated, 

 so far as posterity is concerned, so that we have to 

 deal only with the chance matings among the fertile 

 gametophytes (XO and OY). According to mathe- 

 matics there are four possible matings between these 

 two gametophytes (fig. 33). Out of these four result- 

 ing F 2 sporophytes two would evidently produce only 

 fertile gametophytes and would remain fertile as long as 

 they are inbred. The other two are exactly like the 

 original F x hybrid and therefore semi-sterile, giving 

 one-half sterile gametophytes. The whole dynasty 

 may be represented as follows: 



P Fertile X Fertile 



> 



Fj Semi-sterile 



F a 



F 3 



I 1 



50% 50% 



v 



F 4 Fertile Fertile Fertile Semi-sterile 



This is a very ingenious scheme and, like others, 

 should be tested by further experiments. To a certain 

 extent it has already met this test, for BELLING (2) 

 has subsequently reported a few more generations 

 in which the breeding results were entirely consistent 



