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the botrytis infestans , be the true parasite of the potato, it is not only en¬ 
tirely subaltern in its character, but its very existence hangs upon the living 
tissue of the plant. It is so fleeting and evanescent that it can only seize 
and fix, in its mobile vitality, upon some extrinsic and superior law of 
life. The plant upon which it preys must forever precede it in the ad¬ 
vancing scale; and when it has reached its ultimate point of development, 
its dynamical forces must give way to those of the superior life. It will 
then fall back to its retrograde point and await the restoration of the nu¬ 
tritive plant. Instead of being a power fully adequate to the destruction 
of the plant itself, it is wholly dependent upon it for its vitality. The 
plant is the only nidus for its seeds ; the only source from which it can 
draw its life. The danger is not then from the loss of the plant, but 
1 from that of its parasite. 
The prevailing opinion, in regard to the character of fungi, seems to 
be, that they are developed from the unhealthy conditions of the superior 
plants, and possibly from some slight chemical changes previously effected 
in their constitution. Their office seems to be to hasten decay after it is 
commenced, and not to produce it in the first instance. They result from 
decomposition and decay, and not in those conditions. They do not spring 
from the living tissue and destroy it, but wait till the vital principal ceases 
its action and a chemical change ensues. They are evidently, then, not 
the cause of disease, but the result of it. If the disease were propagated 
by the diffusion of seminal fungi in the atmosphere, it is evident that it 
would march in the direction of the wind, and particularly its stronger 
currents, and that the fields lying along the atmospheric belt wmuld be 
almost simultaneously affected by it. There would be no occasion for 
such great irregularities and inequalities in the distribution of the fungal 
animalculae, or for such apparent partiality of influence as is every where 
manifested through the infected stratum. The fungal virus, or whatever 
may be the producing cause, does not communicate itself through the 
medium of effluvia, or even the secretions of individual tubers ; for tubers 
will remain perfectly sound, or at least without any traceable signs of 
decay, when completely enveloped in the matter of the diseased tubers. 
If there were any external epidemical cause resulting in disease, it would 
go on augmenting until it had either resulted in the destruction of every 
tuber in the hill, or become counteracted by some influence more power- 
