CHAPTER XXXV. 



POTATO DISEASE, I. 

 Peronospora, infestans, Mont. 



ITS ACTIVE STATE. 



THE question is often asked, When did the potato disease 

 first appear ? No one is able to answer this question. 

 The fungus which causes the disease is, like the potato 

 itself, of exotic origin. Peronospora infestans, Mont., 

 grows on the wild potato plants of Peru. The strong 

 probabilities are, that ever since the potato plant has 

 existed, there has also been the putrescent fungus to prey 

 upon it. The family of parasites to which the potato 

 fungus belongs existed in geological times, long prior to 

 the potato plant or any of its relatives. 



It is important to remember, in the consideration of 

 this subject, that the potato and its immediate allies are 

 not the only plants destroyed by the potato fungus, for 

 various members of the family to which the potato belongs 

 also fall before the parasite. Of late years, in some dis- 

 tricts the out-of-door cultivation of the tomato, Lycopersi- 

 cum esculentum, Mill., has been quite stopped by the 

 ravages made upon it by the potato fungus. All the 

 species of Lycopersicum, of which we have at least eight 

 forms in our gardens, are commonly attacked by the fungus 

 of the potato disease. Sometimes the pest may be seen 

 growing upon the henbane, Hyoscyamus niger, L., or com- 

 mon bitter-sweet, Solanum Dulacamera, L., of our hedges ; 

 at other times it may be observed upon various other species 

 of Solanum, as S. demissum, Lind., and S. cardiophyllum, 



