236 



THE AMEBIC AN NATURALIST [Vol. XLVI1 



Himalayan — HH 

 Albi no — AA 

 F t HA- 



7hH 



1 .4 J. - 



An explanation similar to the second one above has been given 

 by de Meijere ( 10) for Jacobson's results with Papilio Memnon. 

 The evidence on this case is, however, very incomplete, and there 

 are complications due to sex. Either triple allelomorphs or 

 complete coupling would seem to cover the facts as we have them 

 at present. Shull (11) has also used a system of three allelo- 

 morphs for a case in Lychnis dioica. I shall refer to this case 

 again. 



It will be seen that triple allelomorphs may be substituted for 

 complete coupling as an explanation of any case where only 

 three of the four combinations possible on the complete coupling 

 scheme are known. But if we have the double dominant, both 

 single recessives, and the double recessive, then triple allelo- 

 morphism will no longer work. Thus, if a race of albino rabbits 

 is discovered which produces self when mated to Himalayan, 

 complete linkage will be the most likely explanation of the case. 



There are certain other cases which fulfil the above require- 

 ments. Emerson ('11) has reported a case in beans (green 

 leaves— green pods, green leaves— yellow pods, and yellow 

 leaves— yellow pods are the three races concerned). The similar 

 cases of complete linkage reported for corn by East and by 

 Emerson are probably more easily explainable by linkage than 

 by multiple allelomorphs, as, at least in some cases, all four pos- 

 sible races are found. Baur (12) has a case in Aquilegia, 

 where three types of leaves are found— green, variegated (green 

 and yellowish green) , and yellowish green. These behave toward 

 each other in a manner exactly similar to that of the self, Hima- 

 layan and albino rabbits. Finally, Morgan ('12) has reported 

 a case in Drosophila ampelophila. Red eye is a dominant to 

 eosin and to white, and eosin is also a dominant to white. No 

 two types ever give the third when crossed, either in F, or in F 2 . 

 The explanation which has been given in beans, columbines and 

 flies has been that of two allelomorphic pairs, completely linked 

 to each other. 



