208 R. RUGGLES GATES. 



Another pure line of wheat (0290) was also found to be dimer- 

 ous for the red factor in one case and monomerous in another. 

 A race called 0501 was found to be probably trimerous like 

 Swedish Sammet. Nilsson-Ehle considers it scarcely probable 

 that in these two wheats the same three factors for red are present, 

 and thinks that perhaps many more than three independent 

 factors ha\'e to be reckoned with. There seems, however, no 

 reason for such an assumption. It appears more probable that 

 corresponding chromosomes undergo the same change in each 

 case so that the factors are all homologous with each other, 

 though of independent origin in the different races. 



We may, therefore, account for the origin of the duplicate 

 and triplicate "factors" for red in the Swedish wheats by assum- 

 ing that successive mutations have occurred and that in each 

 case the duplicate or triplicate condition has afterward become 

 homozygous and stable through the repeated self-fertilization 

 occurring in later generations. 



Turning now to the history of CEnothera ruhricalyx, it appears 

 that the original monomerous condition has become dimerous 

 in subsequent generations of culture. And it will be seen from 

 the culture records that this has happened independently several 

 times in different lines of descent. 



It may be worth while first to recapitulate in briefest form the 

 evidence for the original monomeric character of CE. rubricalyx. 

 The original mutant gave an Fi offspring of 12 plants, 11 of 

 which had red buds (R) and one green buds (r). Three of the 

 former selfed produced F2 families in which the ratios R :r were 

 respectively 10:5, 14:6, and 33:11. The sum of these three 

 families is 57 :22 which is close to a 3 :i ratio and could not reason- 

 ably represent a 15:1 ratio, nor could either of the three ratios 

 indi\'idually. Two plants descended from the F2 family which 

 yielded 33:11, a perfect 3:1 ratio were used to cross reciprocally 

 with CE. grandiflora, a green budded species of diverse habit. 

 Since these plants were from a family which was obviously mon- 

 omerous, the Fi from the cross would either be all R (if the parent 

 was homozygous) or R:r in equal numbers (if the parent was 

 heterozygous). The numbers obtained were 30 R:28r in one 

 cross and 79 R: 71 r in the other. Hence the family which gave 



