102 James G. Horsfall 



brownish in color. Later a grayish center is differentiated. Lesions vary 

 in size from almost invisible points up to 10 to 15 millimeters in length 

 and 1 to 3 millimeters wide, depending upon the width of the leaf. 



Although in the field the spots vary considerably in color, still the 

 general aspect is one of a light-colored center surrounded by a margin of 

 reddish, purplish, or brownish hue. Comparison with Ridgway's color 

 standards (1912) give: for the center, hazel, pale ochraceous-salmon, 

 light grayish vinaceous-lilac, pale vinaceous-lilac, brownish drab, and 

 pale brownish drab; for the margin, Sanford's brown, Prout's brown, 

 yellow ochre, vinaceous-brown, taupe brown, anthracene purple, blackish 

 brown (1), and dull purplish black. Typical foliar lesions are shown in 

 figure 24. 



Infections in the greenhouse do not appear to show as dark shades 

 as in the field, especially on the margin. Here colors such as eugenia rer 1 

 van Dyke red, vinaceous-brown, or Indian lake prevail. Seedlings grow- 

 ing in inoculated soil in the greenhouse have been observed to damp off 

 at the ground line after developing the characteristic reddish lesions. 



On leaf sheaths the spots are not so regular as on the blades. Large, 

 irregular, brown blotches usually obtain here, so that the greatest damage 

 probably occurs on the sheaths at the bases of the leaves. 



Etiology 



Name, history, and classification of the pathogene. Helminthosporium 

 vagans Drechs., the causal agent in this disease, was discovered by Charles 

 Drechsler and was first reported in 1922 (1922:35). A year later (1923) 

 he described the fungus as a new species. Drechsler states that the fungus 

 resembles Helminthosporium sativum, P. B. K., the cause of foot rot of 

 wheat, in having thick-walled, dark-olivaceous spores, but it differs from 

 the latter in having larger conidiophores, in growing slower, and in sporu- 

 lating only meagerly on potato dextrose agar. H. sativum spores, when 

 they germinate, produce germ tubes only from the terminal cells, but in 

 H. vagans they arise from the central segments as well. 



Pathogenicity. The writer isolated the pathogene, but no spores were 

 found in cultures on sterilized wheat kernels, oat agar, potato agar, or 

 solidified synthetic media of Coons (1916) and Leonian (1924). 



The pathogenicity of the fungus was demonstrated in two trials by 

 planting seed in soil contaminated artificially with a pure culture. The 

 organism was reisolated from the reddish brown lesions produced on seed- 

 lings which frequently damped-off. The fungus was reisolated moreover 

 from infections that were obtained by using mycelium covered with moist 

 cotton as inoculum. 



