384 W. Batesou. 



of blacks was also definite, being one third of the number of greys. 

 Such families were therefore composed thus: 



9 grey : 3 black : 4 albino 

 3 : 1 



It was C u é n 1 of Nancy (42 b) who first provided a clear and 

 satisfactory account of these cases. V) He pointed out that the 

 appearance of 9 : 3 : 4 in the F., generation was due to a difference 

 in the albino used to produce the F,. He suggested that the 

 grey colour should be regarded as consisting of a colour-factor 

 -\- a determining factor which causes the colour when present 

 to be grey. Black, similarly, would be due to the same colour- 

 factor -+- a determiner which causes the colour to be black. The 

 grey determiner is then regarded as dominant over the black deter- 

 miner. Such a system gives a representation of the facts which 

 makes the F« results intelligible. Cuénot further showed ex- 

 perimentally that such determining factors are actually borne by 

 albinos, and segregate in their gametogenesis, though in the ab- 

 sence of the colour-element it is impossible to distinguish whether 

 an albino bears the grey factor or the black, or both. Hur.'«!t(65) 

 has made extensive and valuable experiments with ßabbits confirming 

 these conclusions on a lai-ge scale. In addition to determiners for 

 the actual colours Cuénot showed that similar determiners exist 

 for several degrees of piedness, those conditions nearer to full or 

 self-colour being dominant over the conditions in which the amount 

 of white is greater.'-) Hurst has proved that this conclusion holds 

 for the colour-pattern known as "Dutch-marking" in Rabbits. 



Very similar phenomena were studied by T scher m ak (97, 101) 

 in the case of Pisiini sativum and Phaseoliis. Using races of Pisum 

 with pink flowers he showed that when they were crossed with 

 certain albinos, F, had the purple flowers of the field i)ea. This 

 change he also perceived must be due to the presence in the albino 

 of some hidden factor which was invisible in the albino; but, on 

 meeting colour in a zygote, the hidden factor could operate and 

 determine the colour, in this case to purple. Such hidden factors he 

 proposes to designate cryptomeres (99). 



Before proceeding further it may be useful, as the point is funda- 

 mental, to show diagrammatically the relation of the 9:3:4 in F._, 

 to the simpler 9:3:3:1. The diagram (Fig. 13) shows the F.^ distribu- 



^) I take this opportunity of mentioning' that Mr. R. H. Lock who was then 

 at Peradeniya, Ceylon, wrote to me independently with the same sug-gestion. 



^) Pied hybrids have so often occurred in crosses between domestic and wild 

 species that there are evident limitations to the applicability of this rule. 



