20 



Minnesota Plant Diseases. 



ularly perennial. The latter include both saprophytes and 

 parasites. The fairy-ring mushrooms are good examples of the 

 former, while of the latter, illustrations are found in those rust 

 fungi which attack balsam fir and other cone-bearing plants 

 and form witches' brooms. The mycelium of the fungus caus- 

 ing smut of grains is of a peculiar kind. It often finds its way 

 into the host plant when the latter is very young and tender, 

 and continues to grow in the delicate growing parts and dies 



FIG. 8. Fairy rings o 



>f a mushroom fungus (probably a Lepiota). Photographed by Dr. 

 Ramaley. 



F. 



behind in the mature tissues. The examination of such a plant 

 would show a mycelium only in the growing part of the stem. 

 When the young grains are formed the mycelium develops in 

 their tissues, completely destroying them and forming smut 

 spores in their stead. 



The mycelia of many fungi are capable of resisting many 

 unfavorable conditions, reviving again immediately upon the 

 return of propitious surroundings. Evidence of such power is 

 seen in any woods when a heavy rain follows on a long period 

 of drought. On all sides one finds fungi improving to the full- 

 est their opportunity of favorable weather. 



