Minnesota Plant Diseases. 99 



fungus is a good case in point. Finally, the fungi may actually 

 aid by special devices the spread of disease. Such devices are 

 seen in the sac fungi where spores are forcibly ejected and so, 

 caught by the wind, are easily scattered. Again, infection may 

 take place not only by spores but also by mycelium, and does 

 so in many cases. This is noticeably true in those fungi which 



Fig. 39. — ^A good example of an epidemic. Potato blight has, within a week, entirely 

 destroyed the potato plants in this field. After Clinton. 



attack trees and particularly root parasites. Contact between 

 a diseased tree trunk or roots and a healthy one may ofifer the 

 mycelium a chance to pass over directly from the one to the 

 other and a successful infection may ensue. Some of these 

 fungi have a special shoe-string-like strand of threads which 

 are especially proficient in effecting mycelial infection. 



