Sept. I, 1920 



Genetics of Rust Resistance 



529 



each spikeiet were examined. The result of this examination, together 

 with the percentage of barren florets, is summarized in Table II. 



Table II. — Number of florets not setting seed in Triticum vulgare, T . durum, T. dicoc- 

 cum, and Fi crosses ofT. vulgare uith T. durum and T. dicoccum 



Variety or cross. 



Marquis 



Preston (Minn. 



Pioneer 



Average . 



r)-4 



lumillo (CI 1736). . 

 Kubanka (C I 2094). 



Acme 



Average 



Emmer (Minn. 1165). . . 



Kubanka (C I 2094) X 

 Marquis. 



Acme X Preston 



D-4 X Pioneer 



Average 



Marquis X Kubanka (C 



I 2094). 

 Marquis X lumillo (C I 



1736). 



Pioneer X D-4 



Preston X Acme 



Average 



Emmer X Marquis . 



Emmer X Preston . 



Average 



Marquis X emmer. 



Preston X emmer . 



Average 



Classification. 



Vulgare. 

 ....do.. 

 ....do.. 



Durum . 



....do. 



...do. 



....do. 



Dicoccum 



Durum X vulgare 



.do. 

 .do. 



Vulgare X durum. . . , 

 ...do 



.do. 

 .do. 



Dicoccum, X vulgare 

 ....do 



Vulgare X dicoccum . 

 ....do 



Num- 

 ber 

 of 

 heads. 



15 

 17 

 26 



16 

 16 

 25 



49 

 4 



9 

 10 



Num- 

 ber 

 of 

 florets 

 exam- 

 ined. 



309 



538 

 494 

 898 

 622 



630 



426 



104 

 262 



I, 692 



135 



296 

 348 



410 

 446 



270 

 94 



Num- 

 ber 

 of 

 good 

 seed. 



341 

 500 

 761 



499 

 464 

 864 

 604 



611 

 206 



62 

 97 



704 



128 

 167 



299 

 293 



62 



Num- 

 ber 

 of 

 very 

 badly 

 shriv- 

 eled 

 seed. 



14 



97 

 9 



17 



25 



Per- 

 cent- 



barren 

 florets. 



3-» 

 5-1 

 5-2 



4-7 



4.8 



5-9 

 3-6 

 2.9 



4-3 



49-5 



35-6 



56.5 

 47.2 



52-7 

 31- I 



49. I 

 46.5 



22. 9 



28. 7 

 25.8 



28.2 

 29.8 



29. o 



The main spike of individual plants of the parent and crosses was used 

 for this study. There was an average of 4.7 per cent of barren florets in 

 three varieties of Tritictim vulgare. In four varieties of T. durum there 

 was an average of 4.3 per cent, while emmer (Minnesota 1165) produced 

 only 2.1 per cent of florets which formed no kernels. Since these are 

 presumably homozygous, it seems fair to conclude that the percentages 

 given show the average number of florets which did not set seed on 

 account of causes other than sterility. 



Three Fj crosses were studied in which a durum sort was the female 

 parent and four in which durum was the male parent. The average 



