A Study of Meadow-Crop Diseases in New York 47 



he set up 26 "formae speciales " in this species. Those on legumes are 

 f. sp. medicaginis sativae on Medicago saliva and M. falcata; f. sp. medi- 

 caginis lupulinae on M. Iwpulina; f. sp. meliloti on Melitotus albus, M. 

 altissimus, and M. petitpierreanus; f. sp. trijolii repentis on Trifolium 

 repens; f. sp. trijolii pratensis on T. pratensis; f. sp. trifolii hybridii on T. 

 hybridum; f. sp. trifolii agrarii on T. agrarium; f. sp. viciae on Vicia sativa 

 and other species of Vicia; and f. sp. pisi on Pisum sativum. Hammarlund 

 predicts, furthermore, that even more forms will be found when those 

 on other species of Trifolium are investigated. 



Blumer in the same year (1925), although maintaining that the forms 

 on Pisum, Lathyrus, and Trifolium are distinct, is inclined to the view 

 that the Trifolium mildew is a single form with the various suscept species 

 showing varying degrees of susceptibility. Considerable evidence, on 

 the other hand, presented by the recent epiphytotic in the United States 

 suggests that even Hammarlund's f. sp. trifolii pratensis may represent 

 a group of specialized races. Haskell and Wood (1924:250) say, "There 

 are good reasons to suppose, particularly on account of the conspicuous 

 character of the mildew, its apparent invasion of new localities, and because 

 of the fact that our native clovers are susceptible, whereas European 

 ones are resistant, that we have to deal with an introduced parasite which 

 has found conditions especially favorable in the United States." Haskell 

 (192(3:369) says further that the appearance of the disease in the Pacific 

 Northwest in 1924 and its increase during 1925 tend to confirm the theory 

 that a new physiologic form of mildew has been introduced into the United 

 States where it has been spreading from east to west. 



Life history. A rather careful review of the literature has revealed 

 little regarding the mode of overwintering and dissemination. The 

 scarcity of perithecia in the East and the South militates strongly against 

 the probability that perithecia are significant sources of primary inoc- 

 ulum. It is likely that the mycelium lives over winter in or on the 

 protected leaves that remain green throughout the winter months. This 

 possibility is made more plausible by the work of Klika (1922:75) who 

 shows that, contrary to the general belief, the haustoria of E. polygoni 

 may pass through the epidermal cells and penetrate into the cells of the 

 palisade and spongy tissue, and even into the vascular bundles. He 

 says that this process occurs chiefly in the older leaves in the autumn. 

 The mildew occurs very plentifully in the autumn so that many infected 

 leaves would be present to go through the winter. If so, then the ques- 

 tion is, why docs not the disease become general until after the first cut- 

 ting? Where does the organism live during spring and early summer? 



The writer desires at this point to indicate an apparent analogy between 

 powdery mildew of clover and late blight of potato. In New York, the 

 two diseases have appeared almost simultaneously during 1926, 1927, 



