41 



head are attacked ; in other cases only a few flowers may produce 

 the smut balls. In this new type of infection no general develop- 

 ment of mycelium occurs in the host and the pathological 

 symptoms of excessive dwarfing, tillering, early production of 

 infected heads, etc. are lacking. The growth of the mycelium 

 is confined to the individual part — flower, panicle or branch which 

 is invaded. If this branch is removed the plant will continue 

 to produce only sound stems and panicles. This new type of 

 infection bears some resemblances to the localized infection 

 found in the common corn smut {Ustilago zeae). In the latter, 

 however, any embryonic tissue of the corn plant may be invaded 

 and the mycelium appears to be strictly local in its cycle of 

 development. There seems to be nothing to correspond to the 

 general systemic infection through the young seedling which 

 occurs in the case of the loose smut of sorghum. 



Investigations with Barley and Wheat Smuts. By James A. Paris 



Studies with the covered smut of barley {Ustilago hordei), with 

 particular reference to the demonstration of specialized races, 

 were continued. In the earlier studies on the influence of 

 temperature and other factors on infection, considerable evidence 

 as to the existence of such races in this smut was obtained. 

 During the past year their occurrence has been definitely proved 

 and to a considerable extent the host limits of at least five 

 distinct races has been determined. Marked differences occur 

 as to the range of host limitation of these different races. Some 

 varieties of barley prove to be susceptible to two or more races 

 of the parasite, whereas other varieties seem to harbor only their 

 own specific race. 



Bunt of Wheat.— h series of experiments w4th the two smuts 

 which cause the bunt of wheat {Tilletia laevis and 7\ tritici) was 

 also carried out. The principal studies were concerned with the 

 environal factors influencing infection. It was found that in 

 general high percentages of infection occurred when the seed was 

 germinated at 5° and 10° C. by both smuts. There was some 

 falling off at 15° C. and a striking decrease in the percentage of 

 infection at 20° C. In some cases the infections were higher at 

 5° than at 10° and in other experiments the reverse w^as true. 



