ON THE PERONOSPORiE. 209 



character as those of Peronospora^ but were, when measured, to 

 the ten-thousandth of an inch, exactly the same in size ; the 

 average number of zoospores in each oogonium is also the same. 

 Smith proposes to call this fungus Pe7vnosporites aiitiquarhis^ and 

 says we have probably in this specimen one of the simple 

 primordial plants of the great family of fungi. 



The Potato murrain was not heard of till 1843, but two years 

 later it had become general in Europe and America ; it seems as 

 if the Potato fungus had previously attacked some other 

 plant, possibly another species of the genus Solanum, but had at 

 that time found a more suitable nidus for its development in the 

 moist and weakened tissues of the cultivated Potato. Professor 

 Church says : — " The native country of the unimproved Potato 

 (Chili and Peru) differs so greatly as to rainfall and other elements 

 of climate and season from Great Britain, that it is not wonderful 

 to find the plant much altered in character by its long cultivation 

 here. Naturally the plant is almost Alpine in its habits, very 

 aromatic, and less watery than the improved varieties which it has 

 yielded in Europe ) and the changes which have been wrought in 

 its nature have rendered it more amenable to the attacks of fungi." 

 The Potato, like all other living things, has a peculiar vitality or 

 vital force, by means of which, if unimpaired, it is capable of 

 resisting disease and of braving the attacks of parasites. But if 

 the vitality decreases, then the Potato becomes liable to disease 

 and to suffer from parasites. This reduction of vital force does 

 not take place suddenly, but comes on slowly, after years of 

 artificial cultivation. The vital force having been thus lowered, if 

 an unusually unfavourable season occurs, the Potato has not 

 enough constitutional energy to resist disease. 



When once disease has been experienced, the vitality of the 

 plant is still more lowered, and will continue to be so. As the 

 disease is known in the native country of the Potato, it has been 

 suggested by Mr. Worthington Smith, and others, that the resting 

 spore may have been introduced into Europe in the guano brought 

 from Peru and the Chincha Islands. It has also been suggested 

 that the old disease, called the Curl, amongst Potatoes, is identical 

 with the fungus disease ; if so, the Peronospora would have been 

 present in Europe many years longer than is supposed at present. 



