We may briefly summarize the leading facts demonstrated in the above paragraph. We have seen that there are different alcoholic ferments. In the fermentation of natural saccharine juices, which, especially when acid, so readily undergo a decided alcoholic fermentation, the ferments originate in certain germ-cells, which are spread in the form of minute spherical bodies of a yellow or brown colour, isolated or in groups, over the exterior surface of the epidermis of the plant, and which are gifted with an extraordinary power of budding with ease and rapidity in fermentable liquids. The presence of atmospheric oxygen is indispensable to the germination of these germ-cells, a fact which explains Gay-Lussac’s observation that atmospheric oxygen is necessary for the commencement of spontaneous fermentation in must.[97] Of these various ferments one deserves special mention—namely, the variety termed _saccharomyces pastorianus_. As is the case with all ferments, when we gather it from the deposits produced in must that has been fermented by its action, it is composed entirely of oval or spherical cells or of short joints. When again placed in a similar must it buds, like all the ordinary ferments, and the buds detach themselves from the joints or mother-cells as soon as they have attained the size of these latter, from which time in the new deposit is reproduced the original ferment-form from which it sprung, and so on. Under certain conditions of exhaustion, however, which may be easily obtained, and which we have already accurately described, the cells undergo an absolute change as regards their capabilities of budding and germinating. Each cell, modified in its structure by the conditions we have mentioned, shows a tendency to shoot out all around its surface, with astonishing rapidity, into a multitude of buds, from many of which spring branching chains, covered in parts, and more especially at the internodes, with cells and jointed filaments, which fall off and bud in their turn, soon to present the forms of the yeast deposit. In this way _saccharomyces pastorianus_ seems to afford a kind of bond of union between the race of ferments on the one hand, and certain kinds of ordinary fungoid growths on the other. Of these latter the plant which De Bary has named _dematium_, and which is generally found on the surface of leaves or dead wood, more especially, however, on the wood of the vine at the end of autumn, the time of the vintage, presents a striking example. There seems every reason to believe that at this period of the year one or more of the varieties of _dematium_ furnish cells of yeast, or even that the ordinary aërobian varieties of _dematium_ produce at a certain stage of their vegetation, in addition to aërobian cells and torulæ, other cells and torulæ which are anaërobian, that is, alcoholic ferments.