472 



possible each of the true fermentations might have an Alga peculiar to 

 itself, and that it was well worth their attention to investigate the sub- 

 ject. Sugar could be fermented into alcohol and carbonic acid — 

 into lactic acid — or into mannite and mucilage. It was desirable to 

 know if a new Alga appeared when the fermentation changed its cha- 

 racter. Dr. W. anticipated that no cryptogamic plant would be 

 found when diluted alcohol was converted into acetic acid bj platina 

 black, because no azotized compound was present to yield nitrogen 

 to the fungus, without which, in all probability, it could not be deve- 

 loped. The acetous fermentation, however, differed in several impor- 

 tant particulars from the others referred to. 



Dr. Douglas Maclagan entertained no doubt from the observations 

 of Mr. Goodsir, Mr. Berkeley, and others, that the fungus present in 

 the diseased potato had originated in the leaves, and been propagated 

 down along the stem to the tubers. He had himself observed, and 

 rudely sketched, an organism in the diseased tubers, which, from the 

 drawings exhibited this evening, he had no doubt was identical with 

 that observed by Mr. Berkeley growing from the stomata of the leaves. 

 There was also, he thought, little doubt as to the nature of the brown 

 matter which pervaded the diseased portions. Although it had not 

 been demonstrated microscopically to be a fungus, the fact of its hav- 

 ing been separated by M. Payen, by maceration, and subsequent boil- 

 ing with diluted sulphuric acid, and its being ascertained to contain 

 a proportion of azote equal to that found in analogous parasitical ve- 

 getable organisms, appeared to warrant the conclusion that it really 

 was of the nature of a fungus. Dr. Maclagan thought, however, that 

 the question as to the nature of the potato-disease was not settled by 

 proving the presence of a fungus in the altered portions. It was still 

 a disputable point, whether the fungus was antecedent to, or conse- 

 quent upon, the morbid state of the tubers ; it was yet doubtful, whe- 

 ther the discrimination of the first advances towards the disease fell 

 within the province of the chemist or the botanist. He had frequent- 

 ly observed, on making sections of affected potatoes, portions in the 

 interior of the tubers in which no discolouration had commenced, but 

 which were in a softened, pulpy condition. A portion of this could 

 at once be lifted out on the point of a knife, and on being subjected 

 to microscopic examination, no fungus or brown granular matter could 

 be observed; but the amyliferous cells of the tuber, and these contain- 

 ed starch grains, were found in a swollen state, as if they had been 

 filled with fluid by endosmose, and the compartments of the cellular 

 tissue had thus become so entirely detached from each other, as to 



