Botanical Society of Edinburgh. ^7f 



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 wliich 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 on 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 to a 

 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 



