126 



The results from this preliminary work indicate also a very wide dif- 

 ference in the susceptibility of these cereals to rot by the various strains 

 of Helminthosporium. Oats, on the whole, are less injured by them 

 than any of the other four cereals tested. Corn and wheat were most 

 often first in susceptibility to certain of the strains, and were also highly 

 susceptible to more strains than were barley and rye. 



Seedlings in Petri dishes inoculated. Aseptic wheat-seedlings were 

 placed on moist filter-paper in sterile Petri-dishes and were inoculated in 

 their basal region in three ways: by placing upon them ( 1) wheat tissue rot- 

 ted by H. No. 1 (pure culture), (2) conidia of this organism, and (3) agar 

 bearing an abundance of growing mycelium. No difference was observed 

 in the effectiveness of the three modes of inoculation. Each gave a 100% 

 infection, always visible with a hand lens in 2 days (Fig. 16) as a small spot, 

 which could usually be seen at the same time without a glass. A longer 

 time than two days was necessary to demonstrate that this spot would 

 develop into a general rot, but so it did in all cases when the environ- 

 ment was favorable. 



Seedlings in rag doll inoculated. Wheat seedlings with shoots 2-3 cm. 

 long were placed in a special form of rag doll (PI. XXXIII) and inoculated 

 with H. No. 1 by placing an oese of conidia-suspension on the base of each 

 shoot without wounding. Infection was apparent to the naked eye in 

 every case in two days, and the results in six days are shown in PI. 

 XXXIV. Rotting occurred in 6-12 days under favorable conditions. 

 At 6 days the roots were often more or less blackened for long distances and 

 the cortex filled with mycelium. Views of cross- sections showed a heavy 

 infection of the second leaf, and the sheath completely occupied. With 

 excessive moisture, seedlings were killed by the Helminthosporium in 6 

 days; but if in comparative dryness, only small lesions resulted. Seedlings 

 similarly placed in rag-doll but atomized with conidia-suspension also gave 

 100% infection, and the infection was much more widely distributed. 



Inoculation by diseased tissue or by fungus-bearing agar was in no way 

 superior to inoculation with conidia. 



Control, or check, rag-dolls, made in the same manner but without 

 inoculum, at 2 and 6 days showed no lesions even under microscopic ex- 

 amination. In a very small number of cases there was infection by Hel- 

 minthosporium in the checks, and in a few instances overgrowth by a 

 Helminthosporium similar to H. No. 29, with geniculate conidia. 



Roots of wheat inoculated. Conidia of H. No. 1 were placed on the root- 

 hairs of wheat-seedlings in rag doll. At the end of 4 days all roots so in- 



