346 



Kansas State Board of Agriculture. 



FIG. 291. Downy mildew of alfalfa. Same as Fig. 290, but greatly enlarged, 

 showing the tufts of the fungus. 



These threads penetrate the vital layers of the roots. Later the roots 

 begin to rot and the outer layers slough off. (See Fig. 294.) About this 

 time little roughened knots about the size of a pin-head begin to form in 

 the violet mass of fungus threads. (See Fig. 295.) These are part of the 

 fungus, and tide the disease over from year to year, and are said to have 

 the power of remaining alive in the soil for two and three seasons. 



The disease starts from a center of infection. From this center the 

 fungus grows in all directions through the soil, killing the plants as it 

 progresses. Each year finds the circle growing larger, until after a few 

 years large areas have been killed out in the alfalfa fields. (See Figs. 

 296 and 297.) 



