A Study of Meadow-Crop Diseases in New York 55 



These spots are limited by veins to a large extent and are somewhat 

 elongate but not sufficiently to form definitely linear lesions (figure 1Q, 

 B and C). 



Although the color of the spots varies considerably, the general tone is 

 reddish or smoky brown. Comparisons with Ridgway's (1912) color 

 standards show the lesions to be chocolate or warm sepia on sweet clover; 

 olive brown to wood brown on hop clover; deep brownish drab, light seal 

 brown, and Hay's brown on yellow trefoil; bister, seal brown, bone brown, 

 and clove brown on red clover; Rood's brown and Prout's brown on alsike 

 clover; and burnt umber, warm sepia, chocolate, and bister on white clover. 

 The agreement of color symptoms on many of the suscepts suggests the 

 identity of the disease. Not only the shape but also the color of the spots 

 on white clover is intermediate between that on sweet clover and red 

 clover. Warm sepia and chocolate are common to the spots on white and 

 sweet clovers, while bister is common to the spots on white and red clovers. 

 Light seal brown is common to the spots on yellow trefoil and red clover. 

 No fresh material of diseased alfalfa leaves was available for color compari- 

 sons, but here also various shades of brown prevail. 



The disease occurs on the stems and petioles as somewhat sunken lesions 

 with colors similar to those of the lesions found on leaves. Such stem 

 infections are serious, since they cause the distal parts to wilt and die. 



An ashy-gray down on mature spots on leaves and stems is a diagnostic 

 sign of the disease. This down is composed of multitudes of spores and 

 conidiophores covering the surface of the lesion. 



Etiology 



Name, history, and classification of the pathogene. The writer has given 

 his reasons elsewhere (1929) for referring the fungus that causes this 

 disease to Cercospora zebrina Pass. It is sufficient here to state that 

 material from all the suscepts found in this State and from all the speci- 

 mens available in herbaria agrees even in minute details with exsiccati 

 type material of this fungus collected by Passerini (1887) himself and 

 distributed by Rabenhorst. In that paper the writer lists the following 

 names as synonyms: C. davisii E. & E., C. helvola Sacc, C. medicaginis 

 E. & E., and C. stolziana Magnus. All these names have been applied to 

 fungi on the various suscepts collected from time to time since Passerini 

 first described C. zebrina. 



Pathogenicity. The fungus has been isolated repeatedly in pure culture 

 from single spores. A photograph of a typical petri-dish culture on oat 

 agar appears as figure 11. Alsike and white clovers have been inoculated 

 successfully with conidia collected in the field and with conidia from pure 

 culture. Although the fungus was not reisolated to fullfill Koch's rules 

 of proof, there seems to be little reasonable doubt of its pathogenicity. 



