120 Glume-Length and Grain-Length in Wheat 



In what follows the phrase "F,^.K grains" refers to the grains borne 

 by those F2 plants which have K glumes and so on, the plant categories 

 in F^ and ^3 being thus identical with those of the glume-classification 

 already described. On account of shed-grain etc, the number of plants 

 in a grain-category is sometimes slightly less than the number in the 

 otherwise identical glume- category. 



In the successive generations the grain-length distributions were : 



Fo. 

 Grain-Lengths of Parent Varieties (F^ . P and F^. K) of the Cross. 



Table of Frequency 

 tr N Distribution 



- 80 — 

 0-66 526 XVIII 



— 25 — 

 0-49 395 XIX 



The grain-length distributions are more smooth than those of glume- 

 length and K again shows less dispersion than P. 



F,. 



like the ^1 glume measurements, those of the grains were lost. 

 From memory and from previously published investigations it is con- 

 cluded that the heterozygote length is roughly intermediate between 

 the parental ones. In the F^, the intermediate or heterozygote grain 

 can, with practice, always be distinguished from P and, K. In some 

 five or six well marked characters, it is a very even blend or inter- 

 mediate between the characters of the parent grain-forms. 



F,. 



In maize, the occurrence of "double fertilization" has been estab- 

 lished. Assuming it in wheat, the expectation is that the endosperm 

 of the grain (like the embryo) will be one generation ahead of the plant 

 which bears it. Later on the question is more fully considered but for 

 the present the grain borne by an F^ plant will be referred to as F^ 

 grain. This convention is in no sense prejudicial and it simplifies the 

 designation of the grains of different generations. 



Table XX contains the grain-length frequency distribution for the 

 complete F^. Comparison with Table XVIII {F,.P) and Table XIX 

 {Fq . K) indicates that : 



(a) The F^ distribution contains no constituent exactly like ^0 • P 

 for the frequency at 10'2mm. is almost zero {F^. Mp = 10-2mm.). 



