We repeated these experiments, using unhopped wort instead and obtained similar negative results. We had previously determined that it was necessary to heat flasks of hopped wort to 70° C. (158° F.), at least, and those of unhopped wort to 90° C. (194° F.) to secure them from further change. In short, contrary to the assertions of M. Trécul, M. H. Hoffmann, and other naturalists, it is not true that the spores of _penicillium_ can change into alcoholic ferment. Regarded from another point of view, growths of pure _penicillium_ will give us some remarkable results, the interpretation of which seems to us to be intimately connected with the physiological theory of fermentation that we shall discuss in a subsequent chapter. It is a question as to the production of alcohol whilst the life of the plant is carried on under certain conditions of growth. If we distil saccharine liquids on the surface or in the body of which we have grown _penicillium_, and repeat the distillation in the manner that we have already described for the detection of the minutest quantities of alcohol, we shall readily find that those liquids frequently do contain a little ordinary alcohol. Moreover, if we regard the quantities of alcohol produced, which are always very minute, seldom exceeding 1 or 1·5 thousandth of the total volume of the liquids, we shall find that there is no fixed proportion between this alcohol and the weights of the plants formed. It is possible, for instance, that we may obtain more alcohol from one plant than from another weighing a hundred times as much. Often, however, when the vegetation is abundant we cannot make out the occurrence of alcohol in spite of the sensitiveness of the process described (p. 78). What can be the cause of these varying results relating to the production or non-production of alcohol in the vegetation of the little plant? The numerous experiments that we have made seem to demonstrate positively that they are dependent upon variations in the amount of air or oxygen that is supplied to the fungoid growths, whether, that is, the vegetating mycelium alone be submerged, or the whole plant with its organs of fructification. When the plant has at its disposal an excess of oxygen, as much as its vitality can dispose of, there is no alcohol, or very little, formed. If, on the other hand, the plant vegetates with difficulty, in presence of an insufficiency of oxygen, the proportion of alcohol increases; in other words, the plant shows a certain tendency to behave after the manner of ferments.