74 



MENDELISM 



CHAP. 



deduced were found to accord with the actual facts of 

 experiment. The Fi birds were all " ticked" whites, and 

 in the F2 generation came white and coloured birds in the 



expected ratio. There 

 seems, therefore, little 

 reason to doubt that 

 the dominant white is 

 a coloured bird in 

 which the absence of 

 colour is due to the 

 action of a colour- 

 inhibiting factor, 

 though as to the 

 nature of that factor 

 we can at present 

 make no surmise. It 

 is probable that other 

 facts, which at first 

 sight do not appear to be in agreement with the " Presence 

 and Absence " hypothesis, will eventually be brought into 

 line through the action of inhibitor factors. Such a case, 

 for instance, is that of bearded and beardless wheats. 

 Though the beard is obviously the additional character, 

 the bearded condition is recessive to the beardless. Prob- 

 ably we ought to regard the beardless as a bearded wheat 

 in which there is an inhibitor that stops the beard from 

 growing. It is not imlikely that as time goes on we shall 



Fig. 13. 



Diagram to illustrate the nature of the F2 generation 

 from the cross between dominant white and 

 recessive white fowls, 



