No. 578] 



SELF-STERILITY 



G, he crossed them reciprocally and tested 60 of the off- 

 spring by pollinating from the parents, on the parents, 

 and inter se. The back crosses of (B X G) or (G X B) 

 with B and with G apparently indicated four classes about 

 equal in size with reference to gametic compatibility: 

 (1) plants fertile with both B and G; (2) plants fertile 

 with B but not with G; (3) plants fertile with G but not 

 with B; (4) plants fertile with neither B nor G. 



To these facts Correns gave a Mendelian interpretation 

 by assuming the existence of two factors each of which in- 

 hibits the growth of pollen tubes from like gametes. Eep- 

 resenting these factors by the letters B and G, it is clear 

 that types BB and GG could never be formed. The orig- 

 inal plants were supposed to be of classes Bb and Gg, re- 

 spectively. When crossed there resulted the four types 

 BG, Bg, bG and bg. Plants of types BG, Bg, and bG 

 should be self- sterile, while plants of the type bg should be 

 self-fertile. Plants BG should be fertile with plants bg. 

 plants Bg should be fertile with bG and bg, and plants bG 

 should be fertile with Bg and bg. As a matter of fact 

 Correns 's results were not clearly in accord with the 

 theory. Plants of the type bg were not self-fertile, and 

 the other classes of matings showed many discrepancies. 

 It is only fair to say, however, that the author recognized 

 some of these difficulties, but believed them to be due to 

 other inhibitors. 



In a part of Compton's (1913) work, a still simpler 

 interpretation of self-sterility is offered, at least for a 

 particular case, that of Reseda odorata. Darwin 's origi- 

 nal discovery that both self-sterile and self-fertile races 

 of this plant exist was confirmed and the following results 

 obtained in crossing experiments. Self-sterile plants 

 crossed either with self-sterile or with self-fertile plants 

 gave only self-sterile offspring. Certain self-fertile 

 plants, however, gave only self-sterile offspring when self- 

 pollinated. Other self-fertile plants gave ratios of 3 self- 

 fertile to 1 self-fertile offspring when self-pollinated, and 

 ratios of 1 : 1 when crossed with pollen from self-sterile 



