128 



the cortical tissue was seen to be crowded with Helminthosporium myceli- 

 um coursing mainly in the longitudinal direction of the root. The mycelial 

 threads within the root cortex were remarkably thick 13/z. Wheat seedlings 

 2 cm. long, atomized with conidia suspension of H. No. 1, in 6 days were 

 covered with infection spots over their whole surface. 



Inoculations in soil. Vials 12X70 mm., prepared as described on 

 page 180, were used as containers. Wheat seeds were germinated asep- 

 tically, and when the shoot was about 2 cm. long they were inoculated 

 and transferred to the soil in a vial. The results differed in no essential 

 way from those described for the rag-doll inoculations, though the plant 

 could be kept longer under observation since it was not solely dependent 

 on the seed for food. Aseptic wheat-grains were also planted in these 

 vials with the inoculum placed in three different positions: (a) on the seed; 

 (b) 1.5 cm. above the seed; (c) 1.5 cm. below the seed. When on the seed, 

 lesions occurred low; when above the seed, they were higher; when below 

 the seed, no lesions were on the stem in early days but the roots were 

 heavily infected. 



Duplication, in pots and in benches, of all the above experiments 

 made in vials gave identical results. 



Recovery of Organism 



After all the types of inoculation mentioned above, the organism used 

 in the inoculation was clearly evident in the tissues and producing conidia 

 upon them, and by dilution-plating it was recovered from them. During 

 such recovery there was sometimes evidence of bacterial or other contami- 

 nation, but in most cases of each type of inoculation no contamination 

 occurred, and the pathogenic changes noted were clearly attributable to 

 the fungus used in the inoculation. 



INFECTION PHENOMENA ON WHEAT 



Conidia of H. No. 1 and of H. No. 14 when placed on wheat in rag 

 doll germinated from one or both ends as described elsewhere. The germ- 

 tube grew rapidly, branching freely, and oriented itself lengthwise of the 

 shoot more frequently than crosswise or obliquely, often following length- 

 wise the boundary between two wheat-cells. At certain places where this 

 mycelium touched the wheat-surface it swelled slightly, producing a round 

 or oblong appressorium. These appresoria sometimes, probably most often, 

 arose by the simple swelling of a cell of the main thread (Fig. 17), though 

 frequently also from short lateral branches (Fig. 17, d) or where the terminal 



