342 DISEASES OF ECONOMIC PLANTS 



tirely in destruction of green tissues and impairment of 

 starch-making power. 



The sori, confined ahnost entirely to the leaves, are those 

 characteristic of the rusts, the brown summer spores appear- 

 ing first in linear sori, and the black winter spores coming 

 later in the season. The cluster-cup stage is found upon 

 the wood sorrel (Oxalis). 



Yellow leaf disease, helminthosporiose ( Helminthosporium 

 inconspicuum C. & Ell.). — This blight gives a somewhat 

 frost-bitten appearance to the plants, producing also a thin 

 olive-green mold upon the lower sides of the leaves. Some- 

 times only the tips of the leaves are affected, but usually 

 whole leaves die. 



The disease produces elongated yellowish spots limited 

 by the veins. The spots are sometimes covered with dark- 

 colored spores. The disease is confined almost entirely 

 to late-planted corn, -and is prevalent during its early 

 growth, though it has never been reported upon seedlings. 



It is known to cause much loss in Delaware, New York,* 

 and Connecticut,^ and is of widespread occurrence in the 

 United States. 



Sclerosporose (Sderospora macrospora Sacc). — This 

 causes considerable injury to corn in Italy. It has been 

 collected in the United States, but has not been serious. 

 The tassel is chiefly affected. 



MILLET 



Piriculariose (Piricularia grisea (Cke.) Sacc). — Upon 

 the lower leaves the disease occurs as a spot which is 



1 Stewart, F. C, N.Y. (Geneva) Agr. Exp. Sta. Rpt. 15, 452. 

 « Conn. State Agr. Exp. Sta. Rpt. 13, 171, 1889. 



