HEMIBASIDIOMYCETES 383 



The fungus. It has been ascertained, apparently beyond doubt, 

 that the spores may often retain their capacity for germination 

 in the soil for a period of twelve years. The spore balls are more 

 or less spherical in general outline and vary from 17 to 25 fj, in 

 greatest diameter. The spores in a ball may number several, but 

 frequently only one is present. The sterile cells, which usually 

 form a complete envelope, are slightly colored, generally sub- 

 spherical in form, 4-8 /x in length. The germination, which has 

 been carefully figured, commonly conforms to that of this family 

 of fungi (Fig. 193, b). 



Control. Since infected soil is the chief source of trouble, 

 it is practically useless to treat the seed. The most effective 

 method of prevention is that of transplanting the seedlings, the 

 seed having been previously sown in a bed of soil known to be 

 free of smut. Since, however, transplanting is a laborious and 

 expensive process, it is frequently desirable to treat the land 

 or the drill in which the seed are sown, with sulfur, lime, or 

 formalin. The fungicides mentioned have been used in the fol- 

 lowing manner : sulfur and air-slaked lime in the drill at the rate 

 of 100 pounds of sulfur and 50 pounds of lime, or a solution of 

 formalin containing 1 pound of the latter to 30 gallons of water. 



Urocystis occulta (Wallr.) Reb. on rye (Sec ale cereale), is an- 

 other species of this genus of special economic importance in the 

 eastern and north central states. 



