GRASSES OF IOWA.. 



219 



sheaths, leaves and stems are more frequently attacked than 

 the ears, as is shown elsewhere in this paper. The staminate 

 flowers or tassels are especially affected, either a few of the 

 spikelets or a large number, or a very distinct boil makes its 

 appearance below the staminate flowers on the stem. 



The most characteristic appearance of the smut occurs in the 

 ear, forming the so-called boils. This may include the whole 

 ear or only a small part. The smaller ears further down are 

 affected later, in part by auto-infection or from spores contained 

 in the field. 



Fig. 106. Maize smut on leaf . S— Smut boll, leaf very much wrinkled, 

 smut boils contain the spores. ( King.) 



Fig. 107. Tassel showing corn smut boils and spores. (King.) 



The black 



Microscopic characters. — The sooty mass consists of a large 

 number of small bDdies known as spores, that serve for the 

 reproduction of the fungus. These spores are usually round, 

 spherical, somewhat spiny and measure about ^^ (8-13x8-11") 

 inch in diameter. Hitchcock* has given the measurement of a 

 large number of spares. Under proper conditions of moisture 

 these spores germinate. This proceeds best in sterilized rain- 

 water and if kept under proper conditions of warmth, a tube 

 emerges through a pore. The spore consists of an outer wall, 

 which is spiny, and an inner more delicate, the endospore. 

 The tube or promycelium, as it is called, normally bears lateral 



*Hltchcock. Variation In spores of corn smut. Science 22; 353. 



