HYBRIDISATION AND WHEAT HYBRIDS 367 



typically bearded forms of the same race having awns 6-9 cm. long, the 

 F x plants have ears which on careful examination are readily distinguished 

 from those of the beardless parent, the awns of the spikelets of the upper 

 quarter of the ear being generally from 1-5 to 3 cm. long ; the influence 

 of the bearded parent is also visible in the points on the flowering glumes 

 of the lower portion of the ear, for these, though short, are distinctly 

 longer than those of the corresponding glumes of the beardless parent used 

 in the cross. 



It is true that in the majority of cases the " semi-bearded " heterozy- 

 gotes are not exactly intermediate, but have awns much nearer in length 

 to those of the " beardless " than to the fully-bearded homozygous 

 parent ; they are nevertheless distinct from " beardless " plants and can 

 be readily separated from them in nearly all cases by eye inspection alone. 



The F 2 generation from these " semi-bearded " 1 hybrids consist of 

 "beardless," semi-bearded, and bearded plants in the ratio 1:2:1. 

 This has been established by numerous workers, and I have repeatedly 

 investigated natural hybrids between bearded and " beardless " forms of 

 T. vulgar e with the same result. 



A. and G. L. C. Howard have made observations on several crosses 

 between bearded and quite beardless wheats belonging to T. vulgare. 



The F! generation of these crosses had ears with very short tips to the 

 apical spikelets. 



In the F 2 generation were plants with completely beardless ears and a 

 series of forms with awns of various lengths, the ratio of the more or less 

 bearded to the quite beardless examples being 15 : i. 



The character and distribution of the bearding among 986 plants of 

 an F 2 generation is indicated below : 



The dihybrid ratio observed suggests that two factors are concerned in 

 the production of the fully-bearded ear, one factor being responsible for 

 short or " tip " beards, the other when combined with this giving rise to 

 long awns. 



The fully-bearded plants, according to the Howards' view, contain 

 two factors, B and T, the former representing the " long," the latter the 

 " short " factor. 



