316 Nature and Cause of the Potato Disease. 
are unable to trace it as a primary destructive agent of healthy 
life at all. It is seen in diseased plants, but we have no proof 
that it is the cause of the disease ; while, on the contrary, we have 
proof that, by inducing disease^ it makes its appearance. 
The habits and nature of this fungus are indicative of its 
powers ; and we shall now perceive these powers to be very 
limited, and due to certain conditions of the natural elements. 
Thus the light of the sun destroys it, and drought is fatal to it 
also. It thrives only in damp and dull atmospheres, and its 
habits are altogether secret and saturnine. Now as the earth 
appears a depository for the seed, and even a matrix as well, 
under certain circumstances, we can perceive how the seed may 
always be present, and ready to attack any matter prepared for it, 
supposing it to require a particular condition of matter to vege- 
tate in ; but if we admit the general presence of the seed, and 
view it as a destructive agent, we cannot see how its attacks 
should be partial. Again, if we admit the necessity of a certain 
condition of the natural elements, such as wet, want of sun and 
cold to develop it, we admit that, which proves as much a partial 
condition of matter as it does a partial and limited action of the 
fungus itself. 
The habits and nature of the fungi, the condition of the matter 
they are found in, and all our knowledge and experience of them 
as well, therefore teach us that they are not destructive of the 
vitality of plants as a primary cause, but rather that they appear 
in a particular and unhealthy condition of them to prepare them 
for further changes. 
The eel-like animalcules that 1 have mentioned as existing in 
the heads of the boleti are generated in abundance by putrescence. 
I have produced them by immersing whole and cut tubers in 
water for some weeks, and afterwards exposing them to a dark 
and gloomy atmosphere. They are also produced by putrescence 
in any other similar matter, and are therefore not peculiar to the 
potato. All vegetable and animal beings, while undergoing 
decay, are subject to the attacks of numerous kinds of fungi and 
animalcula. We have not sufficient evidence to show where the 
germs of the whole of this minute race of beings exist ; and 
although in some cases we may trace them, yet our knowledge of 
the mass is very deficient. There are peculiarities in the habits 
of these beings. Thus some animalcules and fungi appear only 
in one class of subjects, others again in another class, and inert 
organic matter seems devoted and apportioned to them in sections. 
Wherever their services are required they appear; for no sooner 
is a body, either vegetable or animal, in the state to require their 
presence than these scavengers of organic matter are seen actively 
at work. There is a wisdom in this arrangement, and a bene- 
