A Study of Meadow-Crop Diseases in New York 81 



colored with a narrow dark madder violet or dark nigrosin violet margin 

 (Ridgway, 1912). Sometimes the purple color is faded, so that the 

 margin appears dark brown. At other times the reverse condition obtains, 

 in which case the purple color becomes so dark that it appears almost 

 black. When spots become numerous, the tissue between them is yellowed, 

 and severely affected leaves are killed. 



Etiology 



Name, history, and classification of the pathogene. The causal agent in 

 this disease is the fungus Heterosporium phlei Greg. The original 

 description constitutes almost the only record of the fungus. The reason 

 probably is that the fungus rarely produces spores in the field, and this 

 makes mycological identification difficult. Spores have never been 

 observed in nature by the writer. The fungus is closely related to the 

 genus Helminthosporium, from which it differs in having echinulate 

 conidia, two- to several-septate. Helminthosporium spores are smooth 

 and pluriseptate. 



Pathogenicity. Gregory (1919:578) first completed Koch's rules of 

 proof with Heterosporium phlei. The results obtained by the writer agree 

 with those of Gregory. Several futile attempts were made to isolate the 

 fungus during the summer of 1926, but it was successfully isolated later 

 by sterilizing bits of affected leaves for five minutes in 1-1000 bichloride 

 of mercury followed by a thorough rinsing in sterile water. Success in 

 isolation depends upon transferring a piece of leaf bearing a spot to a 

 tube of agar rather than planting several on an agar plate as is usually 

 done. Thus any rapidly growing saprophyte can overrun the pathogene 

 only in the tube in which it happens to occur. In the first isolation three 

 tubes out of ten showed this fungus in pure culture at the end of two 

 weeks as a minute outgrowth from the piece of leaf tissue. Single spore 

 cultures were obtained subsequently. Oat agar is colored dark purple like 

 the leaf spots. Inoculation with two strains produced the typical leaf 

 spots in ten days on two-months-old timothy seedlings in the greenhouse. 

 The fungus was reisolated from the lesions, and the typical cultural charac- 

 ters of Heterosporium phlei were produced again. 



Life his ory. Almost no data on the life history of this fungus are 

 reported in the literature. It seems to overwinter on the green leaves, 

 as lesions have been observed on these in the early spring before secondary 

 infections could have occurred. 



Spores germinate readily in tap or distilled water in the laboratory on 

 glass slides in about twelve hours, sending out a germ tube from one or 

 both ends. 



