542 On the Nature and Causes of the Decay in Potatoes. 
juices have become mixed and exposed to the action of the air. 
The disease then, according to this view, is some constitutional 
weakness in the walls of the cells, which are unable to resist the 
action of the air. The cells being destroyed, the albumen and 
gluten become mixed with the sugar and gum, and putrefaction 
ensues. 
I have already alluded to the decay which immediately proceeds 
in the grape when its cells are ruptured and its various consti- 
tuents mixed together. Mr. W. Crum of Glasgow, reflecting on 
this circumstance, grated down a potato and observed the progress 
of the pulpy mass in its decay. By thus grating it the cells 
were torn and all the ingredienis mixed together, and exposed to 
the air. It was onl}- doing quickly, what the disease does 
slov.ly. If a potato be thus grated, in a few minutes the pulp 
begins to acquire a reddish colour ; in an hour it is very red, then 
it becomes brov.n, and finally black. In two or three days 
several varieties of fungi begin to appear, in about eight days it 
is covered with a white mould, and finally acquires a most offensive 
smell. This experiment of j\Ir. Crum is a most admirable one, 
and illustrates the progress of the disease even in the various 
shades of colour which the diseased potato assumes. Is not this 
a completely satisfactorj- solution of the nature of the disease ? 
A perfectly healthy potato, in which sporules of fungi cannot in 
the least be detected, becomes in a few minutes tainted with the 
characteristic colour of the disease; the colour changes just as it 
does in the diseased potato itself; and a soil for the fungi being 
established, the sporules floating in the air descend upon the 
mass and grow there. The disease then is simply a decay of 
organic matter, not peculiar to the potato, for I have been 
al^le to produce it in turnips and apples quite as well as in the 
potato. 
By these experiments, then, you must be convinced that the 
disease is a simple decay of the cells of the potato, which by some 
constitutional weakness yield to the action of the air, and allow 
the putrefactive juices to mix together. 
Iliis is a great point to have attained, and the next point is — 
what has produced this constitutional weakness in the cells of^ this 
hardy tuber ? It is quite decided that the potatoes nearest the 
surface of the ground, which by exposure to the heat of the sun 
have become thoroughly matured and even conqjletely greened, 
have, in almost every instance, escaped the attacks of the disease. 
On the contrary, it is found that the lowest tuber, that fur- 
thest away from the overground stem, and therefore most re- 
moved from the action of the light and heat of the sun, becomes 
socmest diseased. Here then we have decisive proofs that the 
disease is in some way connected with an imperfect maturity. 
