68 



In crossings made between sorts which are susceptible to yellow rust 

 and those which are relatively resistant a whole line .of hereditary gradations 

 between the extremes may be produced (52, p. 57-75). Thus in the cross- 

 ing 0208, Extra Squarehead (very resistant) "X 0406, Bore (susceptible), 

 there were found in the third generation only 2 plots out of a total of 72 in 

 which the susceptibility was about as great as 0406 (Grade 4) ; the others> 

 were intermediate, or more or less resistant (Grade 0). 



An exceptionally large number of hereditary gradations, in regard to 

 rust resistance, was produced by the crossing 0406 (Bore) X 0728. The rust 

 grade of the parents together with that of different lines in F 3 is given as 

 follows : 



0406 11/6 Rust, Grade 4 



0728 " " " 2 



0406 X 0728 F 3 -- 6 plots " 



a a u a u -I 



(I f! (I il il it Q 



f) U II U q 



q <( a .'.' it < 



3 " " " " 5 



9 " u u tt f> 



That lines were produced which were both more and less resistant than 

 either parent is clearly shown. 



When the very resistant sort 0319 (Kotte) was crossed with the sort 

 0501 (Grenadier) which possessed an average degree of resistance, lines were 

 produced which, in F 3 were much worse attacked (Grade 2-4) than was 0501 . 

 The sort 0319 being free from rust, during the year of investigation, it was 

 impossible to judge whether or not combinations were produced which, on 

 the average, would be still more resistant than it. 



In crossing susceptible and resistant wheat sorts, Nilsson-Ehle claims 

 never to have obtained results which showed the simple monohybrid com- 

 bination, but rather was the condition more complex. Biffen (9, p. 109), 

 on the other hand, claims that rust resistance follows in segregation, the simple 

 monohybrid rule, viz.: 3 : 1. 



Crossings made between late and early oat sorts have also given inter- 

 esting and significant results. In no case has Nilsson-Ehle found the results 

 to show the simple monohybrid combination, but always a more complex 

 condition as in the case of rusts. An example is afforded in the crossing 

 between 0408 (medium early) X 0450 (late) : 



Result: Out of 112 plots in the third generation there were: 



(a) 4 plots ripening some days earlier than the earlier parent. 



(b) 10 plots ripening decidedly later 5 to 8 days than the later 

 parent. 



The hereditary gradations between the different plots were also 

 numerous. 



