Professor Hansen published some years ago a most interesting memoir on some of the characteristic features of the moulds which are to be found on manure heaps, in which he records how light exerts a very important influence on the manner in which the spore or fruit of these lowly vegetables is set free or distributed. All the various phases in the fructification process of some of these moulds were carefully watched by Dr. Hansen. He kept his caged specimens near a window with an eastern aspect, and he states that in the first instance the stalks inclined towards the light, but that afterwards they assumed an upright position. Darkness was nearly always chosen for the liberation of the spores, but in a few instances a small number were released during the daytime, and it was noticed that when this did occur they were invariably discharged on the side away from the source of light. In various other ways he confirmed this interesting observation, and found that the fruit of the mould was invariably discharged in the opposite direction to that in which the stalk had previously inclined under the influence of light. The force with which the spores were discharged varied very considerably, sometimes being cast to a distance of four inches or more from the stalk, and sometimes being found close to and even on the stalk. The manner in which sunshine may also modify the pigment-producing powers of micro-organisms is remarkable. Many microbes are able to elaborate when grown on various culture media, such as gelatine or slices of potato, most brilliant and beautiful pigments ranging from intense blood-red to the most delicate shades of pink, and embracing every gradation of yellow, as well as browns, greens, and violets. Now it has been found that some of these pigment-producing bacteria, when exposed to sunshine on these nutritive materials, fail to exhibit their characteristic colour, although the duration of insolation may not have sufficed to destroy their actual vitality. One of these organisms originally obtained from water has been specially studied in this respect by M. Laurent. If slices of potato are streaked with a small number of this particular bacillus (_bacille rouge de Kiel_) a magnificent patch of blood-red colour makes its appearance in the course of a day or two, but if, on the other hand, similar slices of potato are exposed to three hours' sunshine, a colourless growth subsequently develops, except where here and there a few isolated spots of pale pink are visible. When the insolation is prolonged for five hours nothing whatever appears on the potato, the bacilli having been entirely destroyed. But this is not all. M. Laurent found that if he took some of the colourless growth and inoculated it on to potatoes he obtained again, but without insolation, a colourless vegetation--in fact, three hours' insolation had so modified the physiological character of the bacillus that _a