112 Shull. 



great. That this purely arbitrary method of compensating for the 

 changing basis of comparison in the different ratios, results in no 

 serious amount of distortion and that it is effective and therefore 

 highly satisfactory, may be judged by the fact that all the curves show 

 a' fairly normal distribution of the variates, and that the large groups, 

 distributed about 75 per cent and 93*75 per cent respectively, in each 

 case cover a range of six classes. 



It should now be easy to interpret figure 5. On the base line 

 the three Fi families are seen in the 100 per cent class indicating the 

 dominance of the triangular type. From this group a single arrow rises 

 to the F 2 group of families, all of which approach the dotted line which 

 marks the position of the 15 : 1 ratio. From this group of F 2 families 

 three arrows radiate to the three kinds of families which appear in the 

 Fs, the one on the left approximating the line for the 3 : 1 ratio, the 

 one on the right having only individuals with triangular capsules, and 

 the middle group repeating essentially the ratios of the F 2 . Each of 

 these three groups of F 3 families bears a different relation to the F^, 

 as seen from the arrows ascending from them to the group of families 

 produced by selfing the dominant individuals in the Fs. The 3 : 1 group 

 at the left has but two arrows, as only two kinds of F* families were 

 derived from this group, while the middle group of the Fs, the 15 : 1 

 group, - produced three groups of F4 families (shown in the upper 

 series), which are seen to be located directly over the corresponding 

 groups of Fs. Above these F 4 groups are still other arrows indicating 

 the relations each group bears to the Fs, this being an exact repetition 

 of the relation between Fs and F4. The discontinuity of the several 

 groups is most strikingly manifest, and can leave no possible doubt as 

 to the fundamental correctness of the method of explanation here adopted. 



This does not, however, exhaust the available tests of the hypothesis 

 that there are two independent determiners for the triangular capsule. 

 There still remains the possibility of showing that the extracted homo- 

 zygotes are not all of the same genotypic constitution as the homozy- 

 gotes used in the original crosses, though indistinguishable from them 

 in external appearance. A reference to figure 4 will make the expected 

 differences clear. Although the triangular capsules are all of the same 

 phenotype, they represent five different genotypes which are symbolized in 

 fig. 4 by the formulae CCDD, CCDd, CcDD, CCdd and ccDD and 

 these five types may be expected to occur in the ratios 1:2:2:1:1. 

 Only the first of them, CCDD, is genotypically identical with the original 

 American biotype used in the crosses. In other words, only one in fifteen 



