112 



Minnesota Plant Diseases. 



the drills. If weather conditions are quite favorable, each new 

 infection increases sufficiently in area to reach over and attack 

 plants in two or three adjacent drills. These infection areas are 

 nearly always circular in outline, and become much enlarged if 

 flax is seeded there the following year. The first year these 



spots may reach a diameter 

 of one to three or four feet. 

 The second year these same 

 areas are usually much 

 more than doubled, so that 

 it takes but three to five 

 flax crops upon such lands 

 to make the infection gen- 

 eral/' 



Diseased fields have not 



FIG. 157.-Sp 01 Psof the flax wilt fungus high- lost their fertility, as was 



ly magnified. After Bolley. formerly SUppOSed, but Can 



produce good crops of 



other plants, as corn, wheat, potatoes, etc. The d'sease seems 

 to thrive on strongly alkaline lands and often under conditions 

 of drouth. 



FIG. 158. Flax wilt. The wilt fungus threads around the root of an at- 

 tacked flax plant. Highly magnified. After Bolley. 



The fungus is an imperfect fungus and lives normally as a 

 saprophyte but becomes on occasion a destructive parasite. The 

 fungus threads live in the tissues of the flax plant root, coming 

 to the surface of the root to produce its spores. The latter are 

 formed in a loose weft arrangement. The ordinary spore is 



