78 Mendelian Inheritance and Yelloin Rusf in Wheat 



If, however, the results obtained from the F^ cultures are applied to the 

 number of plants placed in the different grades of attack in the Fo, we find 

 that the 1:2:1 ratio is very clearly demonstrated. The details of this 

 iipphcatioii are set out in Tables IX and X, and show that the probable 

 composition of the aiitiiinn-sown portion was approximately: 



■2i)-2 DD : 419Z)/? : 208 RR, 



and (if tli(> sprinji-sown ]K)rtion of the Fo generation: 

 189-7 DD : ;378-2 DR : Hi.'M RR. 



Table X. Approximate genetic constitution of the F^ generation {spring- 

 sown portion) as regards susceptibility to Yellow Rust. The.'^e figures 



are arrived at bi/ the direct application of the F^ results. 



* For rust grades see p. Gl. 



The total number of plants was 1560, and the numbers expected 

 according to the 1:2:1 ratio are (;}9()) : (780) : (:59()). Applying the F3 

 results to the wliole F^ crop, we (Ind tlie following cotn])osition indicated : 



391-7 homozygous susceptible individuals. 



797-2 heterozygous susceptible individuals. 



.'>71-1 homozygous imnmne individuals. 



6. Results obtained from F2, F^ and ^^4 ctiltures, etc., in 1920. 



Tli(^ foregoing results were supplemented by further data obtained 

 (luring 1920. All the rust cultures of that year were grown on the Uni- 



