On the Nature and Causes of the Decay in Potatoes. 539 
VVlicn wine is to be made the grape is crushed ; and bj this 
means the easily decaying gluten is mixed with the sugar which 
had in the fruit been kept in distinct cells. Now decay goes on, 
known as fermentation, until at last it results in putrefaction. In 
bruising the potato or the apple a similar mixture of ingredients 
kept separate in the whole potato had been effected, and therefore 
the decay went on. 
The advocates of the fungous origin of decay then brought 
forward a new class of arguments in support of this view. They 
took a sound potato and inoculated it with a diseased one ; and 
that which was sound became also diseased. We have planted 
the fungi, said the}', in the sound potato, and lo ! the disease ha.s 
come. The demonstration was ingenious, so we made another. 
Sour milk is merely milk which is partially decayed , and surely 
no one will aver the decay in this case to be due to fungi. Well, 
on putting an ounce of sour milk in pounds of fresh milk, the 
latter soon becomes sour. Here is an inoculation of decay where 
fungi are out of the question. Putrid meat decays fresh meat, 
because the burning or decay is communicated, just as the flame 
of one candle will communicate the flame to another, without the 
future combustion being in any way diminished by doing so. So 
also a rotten potato may infect a diseased one, just as sour milk 
will infect fresh milk, and the disease may be unconnected Vvilh 
fungi nevertheless. 
The experiments brought forward by the fungus theorists are 
not proofs ; and therefore let us consider the arguments which, to 
my mind at least, have brought conviction that the disease is a 
simple decay of the tuber. In the first place, if the disease were 
a fungous growth, from its commencement ^ve ought to have evi- 
dence of the presence of fungi. Now not the slightest trace of 
their existence can be detected in the first stages of the disease, 
even when that is very decided. It is not until the potato is in a 
very advanced stage of decomposition that either the mycelium, 
sporules, or the fungi themselveis are to be detected. If then no 
proof of their presence can be given, when there is abundant 
proof of the presence of the disease, is this not an a priori argu- 
ment for considering them its consequence, and not its cause ? 
Besides, if they were the cause, when we remember what myriads 
of germs must be floating in the air ready to be taken in by the 
breathing pores of the leaves of every plant in the field, how 
comes it that while frequently the half of one field is quite tainted, 
the other half may be unaffected ? The fungi in their 'creation 
must be coeval with that of the potato, and yet they never exerted 
such a virulent action upon them in any former period of their 
history. Something there must have been in the present year to 
favour their rapid growth, and if such be the case, that something 
VOL. VI. 2 o 
