276 Botanical Society of Edinburgh. 
demic. Although we may not have discovered the causes of epidemic 
diseases, we know they depend partly on local or individual circum- 
stances which may be obviated, and which influence some epidemics 
more than others; and partly to general influences, commonly sup- 
posed to be atmospheric, but regarding which we actually know no- 
thing but their existence. Mr. Goodsir then alluded to the striking 
general resemblance between the rise and progress of epidemics, and 
the appearance, non-appearance, and increase of fungi from season 
to season. Coupling this analogy with the opinion generally gaining 
ground, that certain epidemics owe their existence to the growth of 
fungi or analogous beings in the animals afflicted, Mr. Goodsir con- 
ceived that we are bound, in our attempts to explain the nature of 
the potato disease, not to overlook the fungi which exist in the dis- 
eased tubers. After stating Mr. Berkeley’s late researches into the 
fungoid nature of the disease, Mr. Goodsir observed, that he was still 
inclined to believe*in the organic nature of the brown matter; and he 
founded his belief chiefly on its peculiar form, and on its position im 
the cells. This view of the nature of the potato disease did not afford 
an indication of cure or prevention, for the diseases with the nature 
of which we are best acquainted are not always those we can most 
certainly cure. It holds out, however, a hope that the murrain may 
not recur. The occurrence of fungi as the cause of disease was 
pointed out in various instances, especially diseases of the skin where 
mycodermatous fungi are seen, diseases of the mucous membrane, 
and diseases of the stomach. The occurrence of cellular plants (To- 
yula cerevisig) during fermentation was also alluded to as corrobora- 
tive of Mr. Goodsir’s views. The paper was illustrated by large 
drawings of the diseased structure of the potato, of the brown gra- 
nules, and of Botrytis infestans, &c. 
Dr. Greville in making a few observations, commenced by paying 
a high compliment to the talents of Mr. Goodsir, and the general 
accuracy of his microscopical researches. ‘‘ With reference to that 
gentleman’s theory,” said Dr. Greville, ‘I see nothing improbable in 
the potato murrain being analogous to epidemic diseases in the ani- 
mal kingdom. In fact the analogies between the two great kingdoms 
of organized matter are so many and so strong, that he might reason- 
ably look for much similarity among some of the phenomena exhi- 
bited in both, with regard to disease. Like epidemics in the animal 
world, the one under consideration has appeared almost simultane- 
ously in various and remote parts of the globe; a fact which seems 
to indicate some atmospheric influence. The real cause, as in the 
case of all epidemics, is involved in the greatest mystery. Possibly 
a union of conditions may have taken place favourable to the deve- 
lopment of the fungus which appears to be invariably present. We 
all know that in the germination of monocotyledonous and dicotyle- 
donous seeds a union of three conditions is essential,—the presence 
of air, warmth, and moisture. If any one of these conditions be 
wanting, the seed will not germinate, but, if otherwise favourably 
circumstanced, will remain in a dormant state for an indefinite pe- 
riod. In like manner I think it not improbable that certain con- 
