124 Glume- Le7igth and Grain-Length in Wheat 



are P. Moreover, no plants are found, in any generation, whose glumes 

 are other than P and yet whose grains are P. That is to say the 

 P-form of glume and the P-form of grain appear to be inseparables, 

 remaining associated throughout the vicissitudes attendant upon the 

 production of F^ and Pg plants. Such characters may be called "genetic 

 inseparables" [cf. "Correlation" as used by Collins (4)]. For the K type 

 the same association prevails. Heterozygous plants (/) present an ap- 

 pearance best described as a skilful blend of the P and K forms. With 

 / glumes, / grains are always found. 



Glume-form or appearance, like grain-form, is the resultant of a 

 number of characteristics and since the resultants are inseparable, so 

 must the" constituents be. Close inspection of a great number of plants 

 (P0-P3) leads to the conclusion that there is a considerable number of 

 such inseparable constituent characters, and a list of them is given 

 below. The simplest view of this matter is that one factor controls all 

 the inseparables. The list is : 



(1) Length of glume. 



(2) Ribs on main lamina of glume. 



(3) Shape of tip of glume. 



(4) Curvature of keel of glume. 



. (5) Consistency of material of glume (P is "papery," K is more rigid), 



(6) Length of grain. 



(7) Shape and size of cross-section of grain. 



(8) The angle at which the embryo of the grain is set into the 

 endosperm. 



(9) Number and length of the hairs at the apex of the grain, 



(10) Distinctness of the outline of the apical pad of the grain 

 (" Gipfel-polster "— Kcke). 



For every one of these characters / proves to be an interparental blend. 

 To test the closeness of the association, the correlation between 

 glume-length and grain-length was evaluated for Pq . P and Fq . K. If 

 r — coefF. of correlation : 



(Po . iT) . r = + 0-348 + 0*044 {N = 395), 

 (Po . P) . r = -h 0-392 ± 0-037 {N = 526). 



The values of the coefficient are, at first sight, surprisingly low. It is to 

 be borne in mind however 'that circumstances of environment which 

 affect grain-length, do not of necessity exercise a proportionate or 



