280 



USTILAGINEAE. 



in a yeast-like manner, but on exhaustion of the nutritive 

 materials, the primary conidia, and even the constituent cells 

 of the promycelium, give off germ-tubes. Conidia are never 

 found on the maize-plant itself, but Brefeld's investigations 

 have demonstrated their production on dung-cultures, so that 

 conidia may possibly be produced on manure-heaps or manured 

 soil, and young plants be infected by them. Brefeld has, 

 by means of germinating conidia, successfully infected maize- 



'^'M'M 



Fig. 151. — Ustitctgo moT/dis. Maize-head 

 completely malformed into smut-boils, which 

 have not yet ruptured, (v. Tubeuf phot.) 



Fig. 152. — Ustilago mapdis. Smut-boils on 

 stem and leaf of a Maize-plant. (v. Tubeuf 

 phot.) 



seedlings as well as growing points and other young parts of 

 older plants. 



Infection may take place on any immature part of the 

 host. The mycelium does not grow through the whole plant, 

 but only inhabits a part in the vicinity of the place infected. 

 The heads are most frequently attacked, with the result that 

 the grain fails to reach maturity, or is destroyed during the 

 formation of fungus-spores. 



Owing to the danger of infection, grain mixed with smut- 

 spores should never be used for sowing ; nor can such be 

 safely used for feeding cattle on account of its injurious effects 

 on them. 



