116 Glmne-Length a7id Grain-Length in Wheat 



there occurred more than one type, and denoting the heterozygote by 

 " /," the F^ ratio is : 



JPa = iT : / : P = 114 : 267 : 101 [= 482 plants] 



= 23-65 %: 55-39 %: 20-95 %. 



[N.B. 487 F^ plants set good seed, but only 482 F^ families were 

 obtained at harvest.] 



From the F^ distribution it is concluded that there are three distinct 

 i'g types. The classification of the F2 plants by means of the F^ should, 

 on the assumption of a one-factor difference between P and K, reveal 

 a 1:2:1 ratio among these types. Actually the ratio (given above) 

 deviates considerably from this expectation, and as Tables V, VI, and VII 

 show, the deviation is not explicable on the basis of selective mortality 

 or sterility. Confirmatory evidence is to be found in Biffen [(1), p. 36] 

 with Polish X Rivet, Backhouse (2) with Polish x Kubanka,and Caporn (3) 

 with Polish X Eloboni. In all three of these cases the evidence for a 

 one-factor difference for glume-length was very substantial, and close 

 approaches to a 1 : 2 : 1 ratio were obtained in the F^. No other expla- 

 nation appears to accord as closely with the results of observation above 

 described as does that of one-factor difference ; and consequently as a 

 working hypothesis it is assumed that either P or K possesses a factor 

 for glume-length which the other lacks, and that the heterozygote is, 

 broadly speaking, intermediate between the parental forms. 



IV. The Measurable Characteristics of the P, 7, and K Glume 

 Types in F^, F,,, and P,. 



In Pa and P3 every plant was classified as P, /, or K. The next 

 step was to evaljiate the measurable characteristics — frequency distribu- 

 tion, mean, and standard deviation — of all three types in Pq, P2, and P3 

 successively. The P (and similarly K) plants of P3 are of two kinds, 

 the one descendants of F^.P (designated F^. P ex Pg . P) and the other 

 of Pa . / (designated F^.P ex Pa . /). For the time being the charac- 

 teristics of P3 . P ex Pa . / and Pg . ^ ex Pg . 7 will not be considered. The 

 measurable characteristics of the three types in the three generations 

 were as follows : 



il7=mean glume-length; cr = standard deviation of glume-length 

 frequency distribution and iV^=the number of observations in the dis- 

 tribution. 



