The Potatoe Plague. 97 
act of fermentation or putrefaction, has lately given rise to 
the opinion that these actions themselves, and the changes 
suffered by the bodies subjected to them, are produced in 
consequence of the developement of fungi, or of microscopical 
animals, the germs, or eggs of which are supposed to be dif- 
fused every where, in a manner inappreciable to our senses; 
they are supposed to be developed when they meet with a 
medium fitted to give them nourishment. 
“Jt is certain that sponges and fungi, growing in places 
from which light is excluded, follow laws of nutrition differ- 
ent from those governing green plants; and it cannot be 
doubted that their nourishment is derived from putrefying 
bodies, or from the products of their putrefaction, which pass 
directly into this kind of plants, and obtain an organized 
form by the vital powers residing within them. During their 
growth they constantly emit carbonic acid, increasing in 
weight at the same time, while all other plants, under similar 
circumstances, would decrease in weight. ITIence it is possi- 
ble, and indeed probable, that fungi may have the power of 
growing in fermenting and putrefying substances, in as far as 
the products arising from the putrefaction are adapted for 
their nourishment.” 
The truth with regard to the appearance of fungi in pota- 
toes is, then, simply this: The disease exists in the potatoe ; 
putrefaction takes place, and these germs or eggs which Liebig 
supposes to be every where, find in the diseased potatoe their 
proper nourishment, and hence they begin to grow. If, as 
is asserted, the germs of fungus are diffused every where, 
why do they not affect all other crops, in a similar manner? 
Simply because other crops are not diseased. But over-ripe 
vegetables, fruit, and decaying or putreftying vegetable sub- 
stances are affected in a similar degree, because they are 
putrefying: they are not putrefying because of the fungus. 
But, admitting for a moment that the presence of fung? is 
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