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live equation is properly balanced there is no danger to be apprehended 
from the elimination of error. The unknown quantity will invariably 
return, ‘smaller by degrees and beautifully less/ to the stenographic 
point from which it was ingeniously started. 
The fungal theory of disease has, also, attracted the attention of a large 
number of scientific men, since the commencement of the ‘rot/ but has 
failed to meet the general approbation of those who have carefully in¬ 
vestigated it. It lacks the number of earnest advocates w r ho support 
the ‘wearing-out’ hypothesis. One reason perhaps is, that it is less 
fanciful in theory, and approaches nearer in fact to the real cause of the 
disease. 
Mildew, or parasitical diseases, is not a new discovery in agriculture. 
It was known by the ancients as an incurable malady: to avoid the ap¬ 
proach of which the people often had recourse to spells and enchantments. 
The mala rubigo, or malignant mildew, is frequently referred to by the 
Boman poets ; to prevent the recurrence of which the ‘great Cato’ seems 
to have suggested the efficacious effects of certain kinds of magic. It has 
long been a common malady on wheat, peas, hops, &c., and on the leaves 
of the peach, the nectarine, and other fruit trees. It has not been con¬ 
sidered, however, as the originating , but rather as the resulting cause of 
disease. It arises, or is supposed to arise, either from the constitutional 
weakness of the plants affected, or from some predisposing causes in the 
atmosphere. But it is difficult to trace any connection between the dis¬ 
ease and the hygrometrical, or other states of the atmosphere; for it has 
ravaged with equal intensity under every sensible condition of that ele¬ 
ment, whether of humidity or aridity. 
In examining the parasitical theory, there is this very consolatory view 
of the matter: that, if it be correct, there is no danger to be apprehend¬ 
ed as to the ultimate extinction of the potato as a species. The great 
compensatory system of nature, which holds all the elementary forces in 
due equilibrium, controlling one by the other, and prescribing to each 
its advancing and regressive limits, gives us assurance that no such dis¬ 
astrous results will ever follow. The parasite holds a subordinate, and 
not a subversive, rank in the order of nature. Its life, instead of beinor 
commensurate with, is wholly dependent upon that of the dominant vege¬ 
table or animal upon which it subsists. If then, that terrible scavenger. 
