538 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



If the three forms A A (or simply A), AB, and B are all different in 

 appearance, it will be a very simple matter to count those of each class 

 and determine whether they occur in the theoretical proportions, 1 : 2 : 1. 

 One such case has been observed by Bateson (:02, p. 183) among 

 Chinese primroses (Primula sinensis). An unfixable hybrid variety 

 known as " Giant Lavender," bearing flowers of a lavender color, was 

 produced by crossing a magenta red with a white flowering variety tinged 

 faintly with pink. By seed the hybrid constantly produces plants bear- 

 ing magenta-red and white flowers respectively, as well as other plants 

 bearing lavender flowers. The numerical proportions observed in two 

 successive seasons are shown in Table I. 



The observed numbers, it will be seen, are quite close to the theo- 

 retical, 1:2:1. 



In cases wherein the hybrid is indistinguishable from one of the 

 parent forms (i. e. in cases of complete dominance of one parental 



TABLE II. 

 Heredity of Cotyledon-color among Cross-bred Peas. 



character), only two categories of offspring will be recognizable and 

 these will be numerically as 3 : 1. But further breeding will allow the 

 separation of the larger group into two subordinate classes, — first, 

 individuals bearing only the dominant character ; secondly, hybrids ; 

 that is, into groups A and A(B), which will be numerically as 1 : 2. 



Observed results are in this case very close to theory. Mendel, 

 by crossing yellow with green peas, obtained, as we have seen, only 

 yellow (hybrid) seed. Plants raised from this seed bore in the same 

 pods both yellow seed and green seed in the ratio, 3:1. (See 

 Table II.) The green seed produced in later generations green seed 



