304 Retrograde Varieties 



wards in the red campion, but lack this capacity 

 in the evening-campion, diverging only until an 

 upright position is reached. The combination 

 of hairs, colors and teeth gives eight groups, 

 and the counting of their respective numbers of 

 individuals gave the following result: 



Smooth white straight 12 6 1.6% 



The agreement is as comprehensive as might 

 be expected from an experiment with about 200 

 plants, and there can be no doubt that a repeti- 

 tion on a larger scale would give still closer 

 agreement. 



In the same way we might proceed to crosses 

 with four or more differentiating characters. 

 But each new character will double the number 

 of the groups. Four characters will combine 

 into 16 groups, fsYO^ into 32, six into 64, seven 

 into 128, etc. Hence it is easily seen that the 

 size of the experiments must be made larger 

 and larger in the same ratio, if we intend to 

 expect numbers equally trustworthy. For 



