r 



Balanced Crosses 301 



two groups would consist of thorn-bearing and 

 thornless plants, in the same numerical relation. 

 Thus, we come to the four groups observed in 

 our experiment, and are able to calculate their 

 relative size in the following way : 



Proportion 



Blue with thorns 3/4 X 3/4 = 9/16 = 56.25% 9 



Blue, unarmed 3/4X1/4 = 3/16 = 18.75% 3 



White with thorns 1/4X3/4 = 3/16 = 18.75% 3 



White, unarmed 1/4 X 1/4 = 1/16 = 6.25% 1 



In order to compare this inference from Men- 

 del 's law and the assumption of independency, 

 with the results of our experiments, we must cal- 

 culate the figures of the latter in percentages. 

 In this way we find : 



Found. Calculated. 



Blue with thorns 128 = 51% 56.25% 



Blue unarmed 47 = 19% 18.75% 



White with thorns.. . . 54 = 22% 18.75% 



White unarmed 21= 8% 6.25% 



The agreement of the experimental and the 

 theoretical figures is as close as might be 

 expected. 



This experiment is to be considered only as 

 an illustrative example of a rule of wide appli- 

 cation. The rule obviously will hold good in 

 all such cases as comply with the two conditions 

 already premised, viz.: that each character 

 agrees with Mendel's law, and that both are 

 wholly independent of each other. It is 

 clear that our figures show the numerical com- 



