Section V, 1919 [143] Trans. R.S.C. 



The Inheritance of Earliness and Lateness in Wheat ^ 



By W. P. Thompson, Ph.D. 



Presented by J. H. Faull, Ph.D., F.R.S.C. 

 (Read May Meeting, 1919.) 



Last year the writer communicated to the Royal Society of 

 Canada some results of experiments planned to determine the in- 

 heritance of the length of the growth period in wheat. At that time 

 the experiments had been carried as far as the second generation of 

 hybrids. During the past summer many families of third generation 

 of hybrids were grown in order to determine the exact constitution of 

 the second generation plants and to test the theoretical conclusions 

 reached. Some of the data on these families are given and explained 

 in the following pages. 



In the previous report it was explained that crosses were made in 

 various combinations between several varieties of wheat which showed 

 different degrees of earliness. If A, B, C, D and E represent the varie- 

 ties in the order in which they ripened, crosses were made between 

 A and B, A and C, A and D, B and D, B and E, D and E, etc. In all 

 cases a blending type of inheritance was found and the range of F2 

 variation extended at least from the mean of the early parent to that 

 of the later. In many cases it extended from the lower extreme of 

 the lower parent to the higher extreme of the higher parent. Some of 

 the data given in last year's report are shown in condensed form in 

 Table I. The variation curves for F2 were uniform, revealing no indi- 

 cation of dominance or simple segregation. It was pointed out that 

 the special value of the work from the theoretical standpoint lay in 

 the special test which it made possible of hypotheses of blending 

 inheritance. An hypothesis put forward to explain the results of 

 crossing A and E can be tested In a way not done hitherto, when we 

 also have the results of crossing A with B, A with D, D with E, etc., 

 where B, C and D are intermediate between A and E. On the multiple- 

 factor hypotheses of blending each successive pair of varieties must 

 differ by a certain minimum number of factors, which can be deter- 

 mined by crossing and the conclusion was reached that when the sum 

 of these differences is calculated it is apparently found to exceed the 



^ Results of an investigation carried on with the aid of a grant from the Hono- 

 rary Council of Scientific and Industrial Research, and published with the permission 

 of the Council. 



Sec. V. Sig. 10 



