Nature and Cause of the Potato Disease. 
315 
thing to spread it about. The earth is its depository, and per- 
haps matrix as well, for there we find it; but although we find 
it in the earth, we have no reason to think it placed there to act 
as a destructive agent of healthy vegetation, or as an antagonistic 
principle with which plants in general have to contend, or, in 
short, to view it as an enemy to vegetable life. But as we find 
this fungus in plants, and see its effects on them, we may ask, 
if it be not destructive of healthy life, how it is that it appears in 
them ? This I shall endeavour to answer. 
We have seen that four kinds of fungus may be discovered in 
diseased potato-plants, and that they appear in different states of 
matter. We have the botritis and fibrous fungi, without change 
of colour ; the radiated, with change of colour preceding pu- 
trescence ; and lastly the boleti, with putrescence only. We have 
here then something like cause and effect, for we perceive that a 
certain condition of matter contains a certain kind of fungi, and 
that the boleti is always the last that makes its appearance, and 
that it only appears when putrescence has set in. From these 
circumstances it may be inferred that different kinds of fun^I 
require different states of matter to appear in, and that the con- 
dition suited to one kind is not suited to another, as we never 
find the order in which they exist inverted. We do not find the 
boleti in apparently sound matter, and the botritis in putrescent, 
but on the contrary ; and their appearance is regular according to 
the condition or state of the matter in which they are found, so 
that the kind even indicates the state of matter. This regularity 
and order of appearance, marked by definite states of matter, 
permits two views to be taken of the subject : — 
1. That each kind requires a certain condition of matter to. 
vegetate in as a matrix, hence the appearance of the different 
kinds in different slates of matter. 
2. That the different states of matter are the effect and not the 
cause of fungi. 
As these views are opposed to each other, I shall briefly con- 
sider the facts we are in possession of, and adopt that as the most 
reasonable which best accords with them. 
The fecundity of the botritis, as we have seen, exceeds all cal- 
culation ; and as it is generated by seed, its origin is unequivocal, 
and its antiquity must therefore be equal to that of all other vege- 
table beings. Now if the botritis be viewed as destructive of 
healthy vegetable life, its attacks would be general, and we should 
find it always in action ; and calculating, from its prolific nature, 
that its increase is as the ratio of its attacks, we have in this 
minute being, if such were its office, a power more than sufficient 
to have long since destroyed the whole vegetable kingdom ; but 
so far is the botritis from possessing such fearful powers, that we 
VOL. VII. 7. 
