HYBRIDISATION AND WHEAT HYBRIDS 397 



was intermediate between the parents, and segregation into long-, 

 intermediate-, and short-grained plants took place in F 2 . 



The extracted polonicums of F 2 showed the same phenomenon of 

 " shift " in the length of the grain as in the glume-length, but the reduc- 

 tion was less, the grains being only about 12-5 per cent shorter than those 

 of the grandparental polonicum. 



Engledow found an increase in pubescence in some of the short- 

 glumed F 2 plants similar to that observed by Backhouse. 



d. T. polonicum x T. turgidum. These wheats have been crossed by 

 Vilmorin, Tschermak, Biffen, Backhouse, and others, and natural hybrids 

 between them have been recorded by Jordan. 



(i.) T. polonicum (Bearded) x T. turgidum (Petianelle Blanche, Bearded). 

 This hybrid was raised in 1881 by Vilmorin. The F x plant (1882) had 

 very long, lax, beardless ears, with empty glumes intermediate in length 

 between the two parents. 



In the F 2 generation (1883) were examples of almost pure T. polonicum , 

 together with forms of T. vulgar e and T. durum. Although both original 

 parents had white grain, some of the segregates had red grain. 



(ii.) T. polonicum ? x T. turgidum $ (" Rivet "). Biffen records the 

 crossing of these wheats, the polonicum parent being the common lax- 

 eared form with rachis internodes 6-6 mm. long, pale yellow glumes, 

 almost or entirely glabrous, averaging about 28 mm. long, and 

 white grains : the turgidum plant was the dense-eared cone type most 

 commonly cultivated in this country, with rachis internodes about 3-6 mm. 

 long, greyish pubescent glumes about 9 mm. long, and reddish grain. 



The Fj had lax intermediate ears, rachis internodes 5-8 mm. long, 

 with pale greyish or dirty-yellow pubescent glumes, intermediate between 

 those of the parents, measuring 17 mm. in length. The grains of the 

 F! plants were red, about 9 mm. long, those of the parents averaging 

 10-1 mm. (Polish) and 7-2 mm. (Rivet) respectively. 



Glume-lengths of 595 plants of the F 2 generation were measured, and 

 the frequency distribution of the several lengths plotted ; the curve 

 obtained was sharply divided into three portions, segregation into 149 

 long-glumed : 304 intermediate : 142 short-glumed plants, suggesting the 

 monohybrid ratio i : 2 : i . 



The plants of this generation bore long, intermediate, and short 

 grains, and segregation into white- and red-grained plants also occurred. 

 Biffen found that the chaff colour of the hybrid and its descendants 

 resembled that of the pale polonicum parent. The blue-grey colour of 

 the Rivet ancestor, which in crosses with some other wheats is dominant, 

 was suppressed in this case and did not reappear in any of the plants up 

 to the sixth generation. 



A Polish wheat with white and practically glabrous glumes was crossed 



