Plate X. represents this ferment, at the commencement of fermentation in cherry juice. In the course of a short time there is nothing to be seen but cells of comparatively small size, disjointed and round or oval, and filaments comparatively short and slender. This appearance is indicated in our drawing by the cells _a_, _a_, _a_. As these latter forms multiply with great rapidity, we soon have to search widely over the microscopic field before we find any of the long forms from which they spring. Instead of the forms given in Plate X., we have only those represented in Plate XI. In other words, the aspect of these ferments changes daily, from the very commencement of fermentation. Thus the yeast would appear to grow smaller, coincidently with the progress of fermentation passing from a condition in which it consists of large cells and long ramified filaments, to a condition in which the cells are small and the filaments short. These changes are principally due to an alteration in the method of budding and in the life-processes of the yeast, which speedily exhibits itself when the air supply is reduced, and not through any intermixture of foreign ferments. So, at least, all our observations up to the present time lead us to believe. As soon as the oxygen has been absorbed the cells which form are oval or globular, and the filaments do not lengthen or become so plump. [Illustration: Plate 11. accharomyces Pastorianus, in course of Regular Growth.] This is, however, not the only cause of these changes in form and aspect, although the presence of air, in greater or less quantity, has a marked influence on the earlier developments of yeast; there is another circumstance to be taken into account, difficult indeed to state shortly, but which is demonstrated clearly by the microscope, and is connected with the actual state of the germ cells. As a general rule the budding of a cell is not an identical process when the cell is quite young, and when it has become exhausted from want of nourishment. Between these two conditions there is a difference which may be compared with that which exists, for example, between a newly-formed grain which would not germinate, and the same grain matured by rest, if we may use the expression, that is, which has been kept long enough for its germination to be possible. In other words, and as far as our subject is concerned, we are not to expect that, by reviving our old yeast cells and putting them to grow with abundance of air, in a saccharine, nutritive medium, we shall obtain the appearance of the earlier developments of the germ-cells on the surface of sweet and acid fruits. We see this clearly in Plate VII., the right-hand half of which represents the recruited budding of cells, such as those represented in the left-hand half, in a medium peculiarly adapted to their vitality, _and in the presence of much air_. As regards the length and size of filaments and cells, there is little appreciable difference between the