USTILAGO 339 



as in the yeasts. This method of increase goes on at an 

 enormous rate in manure heaps, etc., and eventually these 

 minute spores find their way back to the land, in a condition 

 favourable for infecting suitable host-plants. 



USTILAGO (PERS.) 



Vegetative hyphae spreading in the tissues of the host, 

 soon disappearing ; fertile hyphae branched, the spores formed 

 in the interior of gelatinised, clustered, terminal branches ; 

 spores i-celled, on germination producing a short, septate 

 promycelium, which bears minute, lateral, secondary spores. 



Loose smut of oats. This disease, caused by Ustilago 

 avenae (Jansen), probably occurs wherever the oat is cultivated, 

 and in this country is known locally as 'smut' or 'slean.' 

 Before preventive methods were discovered it was estimated 

 by Swingle that the annual loss from this fungus in the 

 United States was not less than $18,000,000. The spore- 

 mass or smut is produced in the ovary, and is dispersed by 

 wind and rain before harvest. Brefeld has shown that inocu- 

 lation can only be effected when the oat is in the seedling 

 state, immediately after germination. Spores adhering to the 

 seed germinate along with the oat, and produce a promy- 

 celium, which bears secondary spores, which inoculate the 

 seedling oat, and grow up in the tissue of the plant until the 

 flower is produced, when the fungus forms its spores, in 

 the form of smut in the ovary. 



A supposed form of this species, called laevis, having smooth 

 spores, has been recorded from the United States growing 

 along with the typical form. 



Spore-mass blackish-brown, soon powdery, formed in the 

 ovary ; spores globose or broadly elliptical, delicately warted, 

 6-8 fj,, or 7-9 X 6-7 ji. 



Var. laevis (Kell. and Swing.), spores smooth and slightly 

 darker in colour than the typical form. 



Close has proved by repeated experiments that sprinkling 

 the seed grain with a one per cent, solution of lysol or of 

 formalin in water entirely prevents smut. 



Brefeld, Nachr. aus dem Klub der Landwirthen ztt Berlin, 

 No. 220 et seq. 



Close, Year Book U.S. Dep. Agric., 1894, p. 414. 



