DOMINANCE 



served also among the surviving young of 

 yellow by yellow parents. 



This interpretation of the 2 : 1 ratio observed 

 in this case is strongly supported by a similar 

 case among plants, in which the evidence is 

 even more complete. A so-called " golden ' 

 variety of snapdragon, one in which the foli- 

 age was yellow variegated with green, was 

 found by the German botanist, Baur, to be 

 unfixable, producing when self-pollinated fully 

 green plants as well as golden ones, in the 

 ratio 2 golden : 1 green. The green plants were 

 found to breed true, that is, to be recessives, 

 while the golden ones were invariably found 

 to be heterozygous. Baur found, however, by 

 germinating seeds of golden plants very care- 

 fully, that there were produced in addition to 

 green plants and golden ones a few feeble 

 seedlings entirely yellow, not variegated with 

 green, as the golden plants are. These, for 

 lack of assimilating organs (green chlorophyl), 

 straightway perished. Clearly they were the 

 missing pure yellow zygotes. 



Some Mendelian characters, while not them- 

 selves heterozygous and so unfixable, are never- 



61 



