Minnesota Plant Diseases. 13 



size. Being limited in size, they often live for a long period 

 through which they produce their reproductive bodies and thus 

 compensate for lack of size. In some cases they produce dif- 

 ferent kinds of spores at different seasons. Such is the case in 

 the fungus which causes rust diseases of grains. The sapro- 

 phyte, on the other hand, has often an unlimited supply of mate- 



FlG- 3.— Strands and storage organs. 1. Strands of a stalked puff-ball (Tylostoma) with 

 young fruiting bodies attached- 2. Strands and storage organs of a carrion fungus 

 (Dictyophora ravenellii). Original. 



rial at its disposal. Moreover, this food material is easily avail- 

 able and large plant bodies can thus be built up. Such is the 

 case with a great many saprophytes, especially those of the 

 mushroom group, pufif-balls, etc. Only one ef¥ort a season may 



