308 THE FUNGI WHICH CAUSE PLANT DISEASE 



parts and eventually becoming dissipated and leaving behind only 

 the naked rachis; spores lighter colored on one side, usually sub- 

 spherical to spherical, occasionally elongate, minutely echinulate 

 especially on the lighter side, 5-9 /i in length. On wheat where- 

 ever cultivated. 



The smut mass is covered at first by a very delicate membrane. 

 Infection is floral as described for U. nuda. 



The spores germinate in water by a long 2 to 3, or even 6 to 

 7-septate, promycelium, often curved. In nutrient solutions the 



FiQ. 223. — U. zeiB, stages in spore development. After Knowles. 



promycelium branches profusely but sporidia are few or are en- 

 tirely absent. 



U. zeffi (Beck.) Ung."' 24' ii»-i2i- 133. i36, 142 



Sori on any part of the corn plant usually prominent, forming 

 irregular swellings from a few millimeters to over a decimeter in 

 diameter, at first protected by a sort of false white membrane 

 composed of plant cells and semi-gelatinized fungous threads, 

 soon rupturing and disclosing a reddish-brown spore-mass; spores 

 ellipsoidal to spherical or rarely more irregular, prominently 

 though rather bluntly echinulate, 8-11 n the most elongate 15 /* 

 in length. 



The germination of the spores, which occurs but poorly in water, 

 was first studied by Kiihn * in 1857. In 1874 Kiihn saw the pene- 

 tration of the germ tubes through the epidermis of the com plant. 

 Brefeld showed that the spores germinate well in nutrient- solu- 

 tions and that secondary spores are formed; also that corn can be 

 infected by the sporidia at any point on its surface above ground 



