In concluding our study of the vegetation of _mucor_ as a mould and _mucor_ as a ferment, we may again remark that the most striking analogies also exist between the preceding observations and those we have seen in the case of _penicillium_, _aspergillus_, and _mycoderma vini_. These latter plants do not furnish alcohol or carbonic acid gas by direct fermentation of the sugar, as long as we let them vegetate with plenty of air at their disposal. Once submerged, however, their vital aspect changes; on the one hand the cells or filaments of the mycelia evince a tendency to become larger; on the other hand there is a tendency to greater closeness in these latter, and, consequently, a transition to the state of _conidia_. Lastly, there is a correlative budding of cells, accompanied by a formation of alcohol and liberation of carbonic acid gas; in short, all the ordinary signs of alcoholic fermentation. The principal difference in the case of _mucor_ consists in this, that the vegetation of this latter, under the conditions of insufficient aeration or none at all, is more decided, both as to extent and duration. It may be thought that all the varieties of _mucor_ are capable of yielding the kind of ferment that we have just mentioned. But this is not the case; and here we have another striking proof of the great physiological differences presented by forms of vegetation so intimately connected with each other that, in botanical classifications, they must be put as closely as possible together. Of this fact we have the most striking example in _mycoderma vini_ and the alcoholic ferments, properly so called, which so closely resemble each other in form and development that they might be supposed to be identical, at least, according to our present knowledge, but which differ so widely in their physiological aspects. On November 17th, 1873, we found a very beautiful specimen of _mucor mucedo_ on a pear, under a glass bell jar. It was a mass of perfectly straight filaments, simple and isolated, very large in comparison with those ordinarily met with, each terminating in a sporange, identical to that of _mucor mucedo_, and proportionately well developed. We are able to distinguish _mucor racemosus_ from _mucor mucedo_ only by the circumstance of its having on its sporange-bearing hyphæ lateral branches which also terminate in sporanges. We sowed only one of the terminal heads of the large erect hyphae in some wort, in which it soon produced an abundant mycelium, but without the least appearance of gas. For a very long time, up to January 7th, 1875, we studied the developments of this organism, which remained all the time perfectly pure, in consequence of our having cultivated it in one of our two-necked flasks on pure wort.