FLAX AND TOBACCO 



157 



These results were explained by supposing that the small- 

 petalled white flax and the common varieties have the same factors 

 for breadth of petal, C, one of the color factors, when alone 

 or in the presence of A is an inhibition factor for flower size. 

 B, when present, prevents the action of C. 



Wilt Resistance in Flax. When flax is grown for several 

 years on the same soil, a heavy infection of Fusarium lini often 

 results, and complete crop failure may occur. Bolley, as early as 

 1901, pointed out the true nature of the disease and devised 



FIG. 35. Selected and non-selected flax on wilt sick soil. Right foreground, 

 non-selected flax killed by wilt; left foreground, selected flax; left background, 

 non-selected; right background, selected. University Farm, St. Paul, Minn., 

 1918. (After Stakman, et al., 1919.) 



methods for its control. Seed treament and crop rotation were 

 shown to be beneficial as aids in the control of wilt. Seed 

 selection, however, proved the most efficient control measure. 

 In general, Bolley (1903, 1909) found that two or three years' 

 selection under disease conditions were necessary in order to 

 isolate a resistant variety. Both individual and mass selection 

 methods were used. Similar studies carried on at the Minnesota 

 Station (Stakman, et al, 1919) have confirmed Bolley's results. 

 One of the peculiar results of this work is the discovery that 

 resistant varieties lose their resistance after they have been 



