6 



downy mildew which causes the well-known rot of the 

 Irish potato. It is now believed that this disease does 

 much less damage in America than has been commionly 

 supposed^ the injury attributed to it being often due to 

 other fungi, but it is sometimes destructive^ and its life- 

 history has been carefnlly studied. 



The first indication of the presence of the downy 

 mildew in the potato field usually is the appearance of 



FIG. 3. DISEASED POTATO LEAF. 



brownish spots upon the leaves. As the disease pro- 

 gresses these spots gradually enlarge, finally involving 

 the whole leaf, which turns dark brown or blackish. 

 Then neighboring leaves become affected, and the whole 

 plant eventually wilts and dies. 



