228 The Sn^jpressioii of C/taracters on Crossiny 



a solitary case has been met with where a rough grey wheat crossed witli 

 a smooth white has given F^ plants bearing rough dark grey and rough 

 white ears. The plants were well developed and thoroughly matured so 

 that there can be no question of the genuineness of the phenomenon. 

 The F„ generation of this cross still has to be raised, and until this has 

 been examined there must be some doubt as to whether similar phenomena 

 are being dealt with. 



In wheats it is possible that the suppression of chai-acters is more 

 general than it appears to be at present. A considerable number of 

 examples are known where recessives make their appearance in F., gene- 

 rations from crosses of parents showing dominant characters only. Thus 

 red-grained varieties crossed together frequently produce white-grained 

 forms even though the parents breed perfectly true to their red colour. 

 In the commonest cases the ratio of red to white is as 15 : 1. The 

 ratio has been thoroughly established by Howards Nilsson-Ehle'-, who 

 first called attention to the fact, has suggested that it is due to there 

 being various red-producing foctors G, Oj, C2, etc. The parent wheats 

 then have a constitution represented by Oc, and CjC and the gametes of 

 the hybrid form four classes CC^, Cc^, C^c, oci. The combination of cCi 

 with cci will thus occur on the average once in sixteen times. Similarly 

 by assuming the existence of three distinct red-producing factors, a ratio 

 of one white to 63 red can be accounted for. Such proportions probably 

 occur from time to time, but a wholly satisfactory demonstration of their 

 existence has not been given up to the present. 



On this hypothesis the highest frequency with which white can 

 occur in such crosses is one in 16. But the ratio of one in four has 

 recently been found in such a cross between Squarehead's Master and 

 a deep red wheat collected in the western provinces of China and at 

 present unidentified. The same cross and another between Squarehead's 

 Master and a corresponding white form of this Chinese wheat has given 

 bearded plants in the Fn generation thcjugh both parents are beardless. 

 The proportions are again aj)proximately one bearded plant to three 

 beardless. 



It is possible that these cases represent terms in a scries beginning 

 with complete suppression of a dominant character, then its suppression 

 once in 4 times, once in 16, once in 64, and so on, but it is difficult to 

 devise methods for testing the hypothesis. 



1 Howard, Mein. Dept. Agr. in India (Botanical Series), Vol. v. p. 1, 1912. 

 ■- Nilsson-Ehle, Kreuzungsuntersuchimyen an Hafer und Weizen, 1909, p. 68. 



