276 DISEASES OF FIELD & GARDEN CROPS. [CH. 



Lind., or on the Petunias of our gardens. Sometimes the 

 parasite may be seen upon an entirely different natural 

 order of plants from that of the potato ; it may leave the 

 Solanacece and prey upon members of the Scrophulariacece, 

 as the New Holland plant named Anthocercis viscosa, R.Br., 

 or, as pointed out by Professor de Bary, the Chilian 

 Schizanthus Grahami, Gill. We have both these plants in 

 our gardens. It is worthy of note that there is a second 

 species of Peronospora met with on Solanaceous plants, 

 named Peronospora Hyoscyami, P., and peculiar, or nearly 

 so, to the common henbane, Hyoscyamus niger, L. 

 Hyoscyamus is by no means common in Britain, but its 

 parasite has been recorded from a single locality near 

 Market Deeping. 



Circumstances might have been, and probably were, 

 adverse in this country to a rapid spread of the potato 

 fungus soon after the first introduction of the potato. At 

 length the time arrived when circumstances changed, and 

 something it is impossible to say what greatly accelerated 

 the growth and vigour of the fungus. When the potato 

 and its parasite were transferred from South America to 

 Northern Europe, the climatic conditions were changed, 

 and the potatoes were grown in a new, artificial, and 

 unnatural manner. The constitution and habit of the 

 potato also became changed, we do not say weakened, 

 although this may be the case, but altered. At the time 

 of the alteration or modification of the nature of the potato 

 plant, the potato fungus acquired greater potency over it. 

 The same phenomenon has occurred with the tomato : as the 

 plant has been gradually altered in habit by cultivation, 

 so the habit of the assailing fungus has varied. There is 

 no evidence to show that the Peronospora has altered in 

 the least in the potency or non-potency of its attacks 

 upon our neglected wild plants. 



The first accounts of the potato disease in Europe are 

 very obscure, but as our business is less to detail the 

 history of the fungus than to describe it with its effects, 



