290 GRASSES OF IOWA. 



extended BurriU's work so that we are now pretty familiar 

 with the nature of the disease. 



The red blotches on the leaves and sheaths are familiar 

 objects to almost every one who has observed sorghum. On 

 the inside of the sheath the color is somewhat intensified, being 

 of a brilliant carmine color. The red blotches are in the early 

 stages somewhat circumscribed, but later they are large and 

 irregular, often elongated. The roots are often affected, more 

 especially in young plants. The disease makes its appearance 

 quite early. On the college farm many young plants from four 

 to six inches high showed yellow blotches exteoding across the 

 leaf; sometifres three or four appeared on leaf; a little later a 

 small purple blotch appeared in the center of the colorless por- 

 tion. Burrill, in describing the disease, says: "Sometimes 

 the appearance of injury is noticeable upon young plants. 

 They grow very slowly, are slender and yellowish in color, and 

 are easily pulled from the ground. The lower leaves die, hav- 

 ing previously shown discolored (yellow or red, mostly the 

 latter) patches on various parts of their surface. Not unfre- 

 quently these conditions prevail in special areas of the field; 

 perhaps several acres, not apparently ditferent in composition, 

 condition of drainage, etc., will have, throughout their extent, 

 this dwarfed and sickly crop, while the rest of the plantation 

 is healthy and vigorous. More often the evidence of disease 

 appears, to a greater or less extent, over the entire field, all or 

 an exceedingly variable proportion of the plant suifering; not 

 unfrequently stalks four or five feet high can be lifted with 

 ease from the soil. " 



The Bacillis sorghl when growing on potato is said to produce 

 a pearly white growth, although there is sometimes a slight 

 tinge of yellow or pink. In old cultures it is said to be of a 

 dirty white and much wrinkled. On agar the growth is very 

 much the same, the margin is usually crenate. In cultures 

 obtained by the writer the growth was dirty yellow; this kind 

 of growth was not only obtained once but several times. It 

 seems therefore reasonably demonstrated that this organism is 

 the cause of the disease, since a specific micro-organism is con- 

 stantly associated with the disease and inoculation experiments 

 made with pure cultures derived from the organism found in the 

 discolored patches have shown, beyond a doubt, that the organ- 

 ism produces the disease. 



*Kellernian. Preliminary report on sorghum blight. Bull. Kansas Agrl. Exp. Sta. 

 5 : 281. 1888. 



