Inheritance of Quanlilative Characters 73 



ratio of 15:1; but in addition to this, among the 15 reds 

 there could be distinguished varying degrees of redness. 

 Nilsson-Ehle suspected that the 15:1 meant a dihybrid 

 ratio, 16 individuals being necessary to give the ratio; so 

 he constructed the tentative scheme shown in fig. 10. 



This shows a regular dihybrid ratio, except that the 

 two factors in^'olved are similar. Applying the single 

 dose and double dose conception, as used in the case of 

 Corren's pink Mirabilis, we reach the following con- 

 clusions: only no. i has four doses and therefore it is 

 deep red; nos. 2, 3, 5, and 9 have three doses and are 

 somewhat lighter red; nos. 4, 6, 7, 10, 11, and 13 have 

 two doses and are still lighter red; nos. 8, 12, 14, and 

 15 have one dose and are very light red; while no. 16 

 alone has no dose and is the only pure white. This 

 accounts for the 15:1 ratio, and the different shades of 

 red. This is of course quite in accord with the Mendelian 

 method of inheritance, only two assumptions being 

 necessary: (i) that dominance is absent, two doses 

 having twice the effect of one; (2) that the independent 

 similar factors are cumulative in their operation. This 

 was Nilsson-Ehle's conception, and of course he tested 

 it by further experimental work, the results consistently 

 confirming his assumptions. 



Since it is important to fix this conception clearly in 

 mind, another type of diagram may represent the facts 

 even more clearly. The proportion of the individuals 

 showing the various degrees of redness in the F2 is 

 graphically recorded in fig. 11, each dot representing 

 one dose of the factors in question. 



Continuing these investigations, Nilsson-Ehle next 

 discovered a new strain of red-grained wheat, which. 



