THE OXIOX SMUT 



151 



the fungus oyer from season to season. They have a 

 thicker wall than the conidia, and are spherical rather 

 than oval. 



Treatment. — The destruction, by fire, of all refuse 

 tops in which the resting spores may pass the winter, is 

 one of the most important remedial measures. Such 

 tops should never be turned under unless the ground is 

 to be used for some other croj) the following year. 

 Rotation of cro-ps will probable pro'.o the most success- 



FIG. GG. DEVELOPMENT OF SPOKES. MAGNIFIED. 



ful general remedy. Where the nse of fungicides is 

 practicable these, no doubt, can be employed to good 

 advantage. 



Literature. — Professor William Trelease published 

 an excellent account of the onion mildew, in 1883, in 

 the first report of the Wisconsin Experiment Station. 

 Dr. Thaxter also has a good discussion of it in the report 

 of the Connecticut Station for 1889 (pp. 155-158), and 



