HEMIBASIDIOMYCETES 



377 



mycelium is rather sparsely distributed throughout the general area 

 of normal tissue, from which swellings arise, but it becomes devel- 

 oped at certain points in quantity in the form of pockets, in which 

 areas it is later differentiated into the spores. Upon the stem the 

 abnormal growth has been 

 found to originate principally 

 just beneath the epidermis, 

 that is, outside of the area 

 of the fibrovascular bundles. 

 Rapid multiplication of the 

 host cells occurs, and these 

 become diverse and always 

 abnormal in form. Neighbor- 

 ing bundles send branches 

 into the abnormal tissue, and 

 the bundles at some little dis- 

 tance may also show consider- 

 able variation from the normal 

 type. At maturity cells of the 

 host are very largely broken 

 down, and the pockets of 

 spores are surrounded by a 

 membrane made up of modi- 

 fied fungous threads mingled 

 together with dried host cells. 

 This membrane is soon broken 

 and the loose spores are set 

 free. The spores are more or less spherical, though sometimes 

 irregular, measuring often 8-12 /x, and the walls are beset with 

 blunt echinulations. The spores germinate readily in water or in 

 nutrient solutions in the normal manner. This fungus is known 

 only upon one host besides the corn, that is, Eachlcena luxurians. 

 One other species of smut is found upon the corn, Ustilago 

 Reiliana, but this is readily distinguished from the common smut. 

 Control. Since this fungus may gain entrance to the host at 

 any time, prevention consists in cutting out the affected stalks 

 before the spores mature. Such stalks, moreover, should be 

 destroyed and not thrown upon the compost heap where the 



Fig. 192. Ustilago nuda: Loose Smut 

 of Barley 



