PHYCOMYCETES 



!53 



was at first probably more or less confined to the Mississippi 

 Valley and states to the eastward. It has been known for a 

 long time as a pest in the Middle Atlantic States, extending 

 westward to the Mississippi, but in the states farther to the 



Fig. 52. Grape Leaf with Early Stage of Downy Mildew 

 (Photograph by H. H. Whetzel) 



northeast, while equally common, it has been less disastrous in 

 its effects. This is to be accounted for in part by the vigorous 

 growth of the vine under more constant rainfall ; but the greater 

 injury farther west has been attributed particularly to the fact 

 that the fungus appears earlier in the season. The disease was 



