174 GENETICS 



ently similar flowers of the black-eyed susan (Rud- 

 beckia hirta). When placed in a solution of KOH, 

 the yellow cones of one kind turn a purplish-black, 

 while the other kind turns red. 



B. PARTIAL POTENCY 



Partial potency covers all cases of incomplete 

 dominance, such as those of the four-o'clock (Mira- 

 bilis) and blue Andalusian fowls, where a simplex dose 

 of a determiner does not produce the same visible effect 

 as a double dose. 



The dominant prickly jimson weed (Datura), when 

 crossed with a recessive glabrous variety of the same 

 plant, produces cross-breds in the first generation 

 which show only a few prickles (Bateson) (Baur), 

 following the law of partial potency. 



Banded and uniformly colored snails also, when 

 crossed together, produce snails with shells showing 

 only a pale banding (Lang). 



Numerous further instances of incomplete domi- 

 nance could be cited. 



C. FAILURE OF POTENCY 



If for any reason a determiner fails to accomplish 

 its possibilities in whole or in part, then the character 

 in question may never become evident, and the result, 

 so far as appearances go, is the same as if it was a 

 recessive lacking the determiner entirely. 



That the failure of potency is not identical with the 

 absence of a determiner can usually be demonstrated 



