390 THE WHEAT PLANT 



again with rye gave an entirely sterile F 3 generation. Jesenko obtained 

 only a single fertile grain from over 4800 pollinations of F x flowers with 

 rye, but he was more successful when wheat pollen was used ; in the 

 latter case about 3 per 1000 pollinations produced viable grain. 



Although these derivative hybrids (F x plants pollinated with wheat) 

 more closely resembled wheat than rye, no two individuals were morpho- 

 logically alike ; some of them were quite sterile, while among the rest 

 there was a great range of fertility, those most resembling wheat being 

 most fertile, 



Jesenko points out that such results must be due to differences in the 

 genetic constitution of the egg-cells, since the pollen used was always 

 the same. He suggests that the carriers of the hereditary characters of 

 the parents are not equally distributed in the eggs of the Fj plant, some 

 receiving more of the wheat " plasma," some less, and in the fertilisation 

 of an egg, containing much wheat " plasma " with the gamete of a wheat 

 pollen grain, the resulting hybrid would more closely resemble wheat 

 than would be the case where union takes place between a similar wheat 

 gamete and an egg containing a smaller proportion of wheat " plasma." 

 In the latter case the hybrid would be less like wheat and more inclined 

 to be sterile like the original F x hybrid, which is half wheat and half rye. 



V. HYBRIDS OF THE DIFFERENT CULTIVATED RACES OF WHEAT 



All the cultivated races of wheat have been successfully crossed with 

 each other. Those in which T. monococcum is a parent are completely 

 sterile ; the rest give fertile progeny, although the degree of fertility is 

 very variable. 



In the hybridisation of T. durum, T. turgidum, T. vulgar e, and T. 

 Spelta, Vilmorin observed forms of all four races among the descendants 

 of hybrids between either of the two former and one of the two latter, 

 from which he concluded that all these wheats had a common ancestor. 



Tschermak obtained similar results in his experiments. Kezer and 

 Boyack found T. Spelta among the F 2 segregates of the cross T. dicoccum 

 x T. vulgare (p. 393), and T. durum appeared in the F 2 of the hybrid 

 T. dicoccum x T. sphaerococcum which I produced at Reading (p. 392). 



i. HYBRIDS OF T. monococcum WITH OTHER WHEATS. Hybrids of 

 T. monococcum with T. dicoccum, T. vulgare, T. durum, T. turgidum, 

 and T. polonicum have been obtained by various workers. Tschermak 

 states that he successfully crossed T. monococcum with all cultivated 

 wheats. 



The hybrids are sterile and have the flat brittle ear, keeled glumes, 

 and marked lateral nerve and tooth of T. monococcum, but show the 

 influence of the other wheats in the larger ears, clearly developed terminal 



