HYBRIDISATION AND WHEAT HYBRIDS 371 



PUBESCENT AND GLABROUS GLUMES. Pubescence and smoothness of 

 glumes usually constitute an allelomorphic pair of characters, pubescence 

 being dominant, and segregation of the F 2 is in the ratio 3 pubescent : T 

 smooth-glumed form. 



In some instances, however, the hybrid (F 5 ) between a velvet-chaffed 

 and smooth- chaffed wheat is more or less intermediate, the degree of 

 pubescence varying considerably ; in these hybrids segregation in F 2 

 follows the 1:2:1 ratio. 



In the hybrid between a pubescent and beardless T. vulgare (Velvet 

 Kolben) and a pubescent and bearded form of T. compactum (Igel) Riimker 

 obtained both glabrous and velvet-chaffed plants in the F 2 generation in 

 .the ratio i glabrous : 3 velvet (p. 403), and a similar ratio of forms with 

 glabrous and pubescent glumes appeared in the F 2 of my hybrid between 

 two pubescent-chaffed wheats, T. dicoccum 9x7". sphaerococcum $ 



(P- 392). 



Pubescence was found to be linked with black chaff in hybrids of 

 Black Emmer with T. vulgare (p. 394) and T. sphaerococcum (p. 393). 



CLOSE-FITTING AND LOOSE GLUMES. In T. dicoccum and T. Spelta 

 the glumes firmly invest the grains, while in T, vulgare, T. turgidum, T. 

 durum, and some other wheats the glumes loosely enclose the grain. 



The close-fitting glumes of T. Spelta are dominant over the loose 

 glumes of other wheats except in hybrids with T. turgidum, in which, 

 according to Kajanus, the close-fitting character is recessive. 



LONG AND SHORT GLUMES. For inheritance of the long glume of 

 T. polonicum see pp. 394-399. 



KEELED AND ROUNDED GLUMES. The keeled character of the glumes 

 of T. durum, T. turgidum, and T. Spelta is dominant over the rounded 

 glume character of T. vulgare and T. compactum. 



BROAD AND NARROW GLUMES. The broad truncated glumes of T. 

 Spelta are dominant over the narrower-pointed glumes of other wheats. 



FORM AND SIZE OF GRAIN. Several of the different races of wheat 

 possess grains of characteristic shape and size which can be recognised 

 without much trouble, although they are difficult to describe. 



The grains of hybrids between the several races usually show the 

 characters of both parents, but little accurate research into the features of 

 hybrid grains has been made except in regard to the grain-length of crosses 

 of T. polonicum with T. durum which was investigated by Engledow. 

 The mean length of the grain of the T. polonicum used was about 10-2 

 mm., that of the durum parent 7-7 mm. 



The Fj grain was intermediate. In respect of size of grain three types 

 were found in F 2 with the following mean grain-lengths : 8-84, 8-67, and 



