The Potatoe Plague. 61 
antee for his talents and ability. This gentleman states the 
result of his investigation to be, that the rot is caused by a 
Sungus, the spores or seeds of which exist in vast quantities 
in the atmosphere, and this opinion has been generally re- 
ceived as true by the best informed circles in Europe. But 
the letter is a document so important to the present question, 
as conveying the prevailing opinions that are entertained on 
this subject in Europe, that we quote it below. 
Mr. Morren, after stating that the evil has prevailed in 
Belgium for several years, though to a far less alarming 
degree than at present, proceeds : 
“The real cause of the evil is a fungus, or sort of mush- 
room, which the learned will classify under the genus botrydis, 
but which agriculturists, without further specification, will call 
a spot, or blemish, or blotches. This mushroom is of ex- 
treme tenuity, but it breeds amazingly, and reproduces itself 
by thousands. Its stems are formed of little, straight, hollow 
threads, which bear on their summits one or more branches, 
always divided into two, and at the end of these branches 
reproductive bodies are found, which have the form of eggs, 
but which are scarcely the hundredth part of a malimetre in 
size. It will be said that this is a very small body to do so 
much mischief; but I answer that the ?fch is not a disease 
the less to be feared because the acare which produces it can 
only be seen by the aid of the microscope. 
After the formation of the yellow spot, and the develope- 
ment of the botrydis on the leaf of the potatoe, the stalk 
receives the deleterious influence. Here and there its epi- 
dermis turns brown, blackens, and, following with the micro- 
scope the phases of the evil, you perceive that it is by the 
rind that the stalk is attacked. The morbid agent carries its 
action from the rind on the epidermis, and though this last 
does not always disclose mushrooms, it is not the less for that 
struck with death. 
6 
