FLA(i Smut of Wheat 



255 



half the height of the former, and has made no evident attempt to 

 form ears. As a riile the plant is attacked so severely that it is unable 

 to produce even young ears; sometimes a diseased stalk does form an 

 ear with grain, but usually the ear is attacked while still very young 

 and enclosed in its leaf sheath. 



Cause of Disease. 



Flag smut of wheat is caused by a fungus, Urocystis fritisi, 

 Koern., and is ne;iily related to other -mut-causing fungi, such as 



Fi<;. U 



e.g., stinking smut of wheat or loose smut of oats. The only parts 

 of the fungus which one can see without the aid of a microscope are 

 the spores or seed-like bodies of the fungus ; these are black, and are 

 readily visible, but only because they are produced in such vast 

 numbers. Each spore itself measures only about one-thousandth of 

 an inch in diameter, so tin. t about a million spores pliaced side by side 

 in a single layer would cover an area of only one square inch. Fig. 

 5 is a drawing of a single spore, magnified about 1800 times, showing 



