m. 644] INHERITANCE OF PLUMAGE COLOR 251 



fore, that tlie two types crossed differ from each other 

 by multiple factors affecting the amount of black pigment 

 produced. The number of these factors can not be esti- 

 mated because of the small numbers of animals involved 

 and because a second generation has been bred only from 

 an original cross in which the Columbian parent did not 

 have the amount of black normal to that variety. Fail- 

 ure to recover the typical Columbian pattern in later 

 generations is probably due to the last named circum- 

 stance rather than the absence of segregation. 



The two varieties probably do not differ by any single 

 factor determining the presence or absence of black pig- 

 ment, but only in the degree to which black is produced, 

 the degree probably being governed by accessory or modi- 

 fying factors. This fact attaches especial interest to the 

 appearance of several birds in the backcross generation 

 which show no trace of black pigment. Do these repre- 

 sent loss of a factor determining the ability to develop 

 any black pigment at all or are they segregates in which 

 factors limiting the exercise of the black-producing func- 

 tion are at a maximum"? Since they are few in number 

 and since variation in the amount of black grades im- 

 perceptibly into the self condition I am inclined to the 

 latter view. If this is true it should be possible to reduce 

 the amount of black in Columbian fowls by rigid selection 

 against it to such a point that birds might be produced 

 which were phenotypically white, but which as regards 

 restriction of buff would breed like Columbians.' Such 

 a character would be in effect a sex-linked self white and 

 the absence of a sex-linked white in the many breeds 

 investigated points to the probability that none has been 

 produced in this way. 



Much of the interest in the case presented here inheres 

 in the apparent sim]ilicity of the results. The crossing 

 of Light Brahnias and Buiff Orpingtons or Buff Ph-mouth 

 Eocks produces in the first, second and backcross gen- 

 erations only two easily distinguishable tn^es, white (Co- 



