304 



THE FUNGI WHICH CAUSE PLANT DISEASE 



and was called U. avense in 1591. The species of Ustilago 

 on oats, wheat and barley were considered identical until 

 Jensen' showed that they are not intercommunicable. Wolff* 

 showed that seedlings can be infected through the first sheath 

 leaf. Brefeld' studying infection more closely found it to be 

 accompKshed by germ tubes from sporidia and that plants are 

 free from infection after the growing leaves have pushed one 

 centimeter through the sheath leaf. The mycelitma, after infec- 

 tion, grows through the plant until blooming time when it seeks 

 the ovaries and the enclosing glumes in which it forms a mycelial 

 mass, which soon changes into spores. In nutrient solutions the 

 conidia bud indefinitely, while on the host plant they produce 

 infecting hyphae. 



Germination was first studied by Provost.' It occurs read- 

 ily in water, a well de- 

 veloped promycelium 

 resulting in about 

 twenty-four hours. 

 Fig. 219. The sporidia 

 are mostly narrowly 

 elliptical. Fusion of 

 sporidia is common. 

 The promycelia are 

 usually four-celled and 

 occasionally branch, 

 especially near the 

 base. " [!«• i2« 



U. crameri Korn.^''' 

 Son in the spikelets, 

 infecting all of the 

 spike, ovate, about 

 2-4 mm. in length, 



Fig. 220.-Growlng point of the stem of barley. <=hi«fly destroying in- 

 Much enlarged, showing smut mycelium. After ^^^r and basal parts: 

 Hftckft 



spores reddish-brown, 

 chiefly ovoid to subspherical though occasionally more elongate 

 and irregular, smooth, with usually pitted contents, chiefly 8-11 n 

 in length. 



