On turning to the lower plants, especially to some species of fungi, one notices a striking contrast in their behaviour to that of the higher plants. Some species of fungi have the power of living and flourishing in the presence of relatively large quantities of copper compounds, or even of copper or bronze in the solid state. Dubois (1890) found that concentrated solutions of copper sulphate, neutralised by ammonia, which were used for the immersion of gelatine plates used in photography, showed white flocculent masses resembling the mycelium of Penicillium and Aspergillus, which grew rapidly and fructified in Raulin’s solution, but which remained as mycelium in cupric solutions. The mould proved capable of transforming copper sulphate into malachite in the presence of a piece of bronze, but it was found that the presence of the latter was not essential for the conversion into basic carbonate. The same result was obtained if the culture liquid was put in contact with a body which prevented it from becoming acid, fragments of marble acting in this way. Copper sulphate solution in the presence of the mould produced a _green_ deposit on the marble, while without the fungus the solution simply evaporated leaving a blue stain of copper sulphate. Trabut (1895) found that on treating smutty wheat with a 2% solution of copper sulphate he obtained a mass of flocculent white mycelium, whose surface was soon covered with aerial branches bearing pale rose-coloured spores, and he gave the provisional name of _Penicillium cupricum_ to the species. On preparing nutritive solutions by steeping a handful of wheat in water for 24 hours, and then adding various amounts of copper sulphate to them, Penicillium was found to vegetate quite well until the amount of copper sulphate reached 9½ grams in 100 c.c., after which the seedings with spores did not develope at all. De Seynes tested this Penicillium more exhaustively with different culture media under various conditions and decided that Trabut was right in only assigning the name _P. cupricum_ provisionally, as the mould reverts to the form _P. glaucum_ when seeded in a natural medium, indicating that _P. cupricum_ has not an autonomous existence, but is _P. glaucum_ which modifies the colour of its conidia under the influence of copper sulphate, in the same way that it often modifies them in other media. It is noticeable that the mycelium arising from the germination of conidia of _P. cupricum_ in a normal medium has a very poor capacity for producing reproductive organs, but this diminished activity is attributed not to a special deleterious action of the copper sulphate but to the impulse given to the vegetative functions, at the expense of the reproductive, when the spores are seeded in a richer medium than the solutions of copper sulphate which serve as the soil for _P. cupricum_.