366 THE WHEAT PLANT 



who obtained a beardless vulgare form among the descendants of the 

 hybrid T. polonicum x T. turgidum, var. lusitanicum (Pe'tianelle blanche), 

 both of which are bearded. 



ii. Bearded x Beardless. In the cross between the bearded T. dicoccum 

 and the beardless T. sphaerococcum (p. 392) the bearded character was 

 completely dominant in F 1} and plants as beardless as the T. sphaerococcum 

 parent were not found in the F 2 or F 3 generations. In other crosses, 

 especially where the wheats belong to the same race, the beardless char- 

 acter is dominant, the bearded recessive. 



As explained elsewhere (p. 104), the term " beardless " includes the 

 rare wheats in which awns are entirely absent from the ears, and the very 

 common group with awns from -3 cm. to about i cm. in length on the 

 spikelets of the upper fourth of the ear. 



In the majority of records of crosses between bearded and beardless 

 wheats the latter belonged to the short- tipped group. The F l generation 

 of such hybridisation has frequently been described as beardless, the 

 beardless character being dominant, and subsequent segregation in F 2 

 was stated to occur in the ratio of 3 beardless dominant : i bearded 

 recessive. 



This view of the inheritance of awns requires modification, since the 

 complete dominance of beardlessness is rarely seen. C. E. Saunders 

 (Report of the Third International Conference on Genetics , 1907, p. 370) 

 referred to the production of semi-bearded plants in the F l generation 

 of crosses of bearded and beardless forms ; out of some 300 of these 

 hybrids he found that : 



15 per cent were more than one-quarter bearded. 

 59 per cent were one-quarter bearded. 

 20 per cent were nearly beardless. 

 6 per cent were beardless. 



Fully-bearded F x plants were not observed, and he says " the number 

 of plants which could fairly be called beardless was very small." 



In F 2 he obtained fully-bearded and beardless plants with an unclassi- 

 fiable series of intermediates. 



No doubt the particular length of awns of the heterozygote F 1 genera- 

 tion depends on the difference of the parent forms employed in the cross, 

 but the fact that beardlessness is but imperfectly dominant is now quite 

 clear. The early inaccurate conclusion of complete dominance of beard- 

 lessness and the 3 : i segregation in the F 2 generation was due to the 

 confusion of what may be termed " semi-bearded " heterozygotes with 

 the so-called " beardless " homozygous plants possessing short awns at 

 the tips of the ears. 



When the latter " beardless " forms of T, vulgare are crossed with 



