Botanical Society of Edinburgh. - 277 
ditions—one or more of them being of a meteorological character— 
may have combined in the course of the past season to promote the 
growth of the potato fungus. The question has been asked, how do 
the spores of the fungus obtain access to the vegetable tissue? ‘This 
at present is a matter of mere speculation. ‘They are excessively 
minute; and it has occurred to me that they, as well as the spores 
of other of the minute fungi, may at all times inhabit the tissue of 
those species of plants to which they are respectively peculiar with- 
out, under ordinary circumstances, deranging the vegetable functions, 
in the same manner as minute parasites infest different parts of the 
animal structure. In addition to this, there must be in plants as 
well as in animals a predisposition to receive the disease; for even 
epidemics make a selection of their victims. The fungus did not 
attack all plants of the potato indiscriminately ; some varieties 
throughout the infected districts having, comparatively speaking, 
escaped,—a most valuable fact for the consideration of the practical 
agriculturist. With reference to the brown granules, which Mr. 
Goodsir believes to be organic, I confess I have been quite unable to 
satisfy myself regarding their nature. Their form is not constant, 
and under the microscope I sometimes find it impossible to distin- 
guish them from the grains of starch. I cannot, besides, detect any 
determinate arrangement of the granules, which the microscopical 
observer would naturally expect to exist in a series of more or less 
spherical organic bodies. Certainly, the brown spots in the tuber 
require more investigation than they (so far as I know) have re- 
ceived. My attention was directed to the potato disease late in the 
season, and no opportunity was afforded me of examining the leaves 
or the stalks. It has struck me, however, in reading Mr. Berkeley’s 
valuable memoir, that the black spots en the stalk, where the cellular 
tissue is described as filled with a dark grumose mass, may corre- 
spond with the brown spots in the tuber, the cells of which contain 
the brown grumose granules, and that the one may throw some light 
on the other.” 
Mr. Walter Crum of Glasgow detailed his experiments on the 
brown colouring matter in diseased potatoes, and stated that it con- 
tained nitrogen. He had carefully examined the brown granules 
alluded to by Mr. Goodsir, but did not believe it was a fungus. 
Dr. George Wilson was much interested in what Mr. Goodsir had 
said in reference to the connexion between the disease in the potato 
and the appearance of a fungus, and in the comparison which he had 
drawn between it and a solution of sugar undergoing the vinous fer- 
mentation in which a cryptogamic plant always showed itself. Dr. 
Wilson was of opinion, however, that the vegetable physiologist was 
not entitled to refer to the fungus as the cause of fermentation, or to 
speak of it as more than an accompaniment. On the other hand, he 
was free to acknowledge, that as the chemist could not point toa 
single example of the vinous fermentation having been observed 
without the Saccharromyces being seen also, he was not at liberty to 
explain the fermentation without reference to the fungus as he ge- 
nerally did. Dr. Wilson believed that fermentation was at present 
