Richter (1901) carried out rather similar experiments. When grown in solutions without and with 1/700,000 gram molecule zinc sulphate the dry weights of the mould were practically the same for the first two days, then the dry weight of the zinc crop shot ahead for a day or two, a depression setting in on the fifth day. Without zinc a less increase took place, and a similar drop was noticeable about the sixth day. The conclusion drawn is that the stimulation due to the zinc occurs chiefly in the first few days and also that the rise in the sugar consumed is more rapid at first with the moulds treated with zinc. Concentrations above 1/600 are harmful, but in weaker solutions zinc is a definite stimulant. Coupin (1903) re-investigated some of Raulin’s work under more antiseptic conditions in order to see what substances were really needed by the mould and whether certain elements declared essential were really so. He concluded that iron and zinc are of no use in the nutrition of _Sterigmatocystis nigra_, but that the zinc retards the development of mycelium when food is abundant, killing it if it is badly nourished. This denial of stimulation was controverted by Javillier (1907) who re-tested Raulin’s solution with extreme care, growing Sterigmatocystis in (_a_) normal Raulin’s solution with zinc, (_b_) Raulin’s solution without zinc. The ratio of crops _a_/_b_ varied from 2·3–3·1 in four experiments, vindicating the favourable action of zinc. With regard to the optimum value for zinc the mould seemed to be perfectly indifferent to the presence of medium quantities but very sensitive to extremes, the maximum weights being reached in dilutions between 1/10,000,000 and 1/250,000, while quantities above 1/25,000 were toxic in their action. At a dilution of 1/50,000,000 stimulation was still evident, though in a less degree than with the optimal concentrations. Javillier maintains that zinc is fixed by the fungus, the whole of the zinc present in dilute solutions being taken up, only part being utilised in stronger solutions. The value of accordance between the quantity of zinc fixed and the quantity supplied decreases rapidly with increase of concentration. Sterigmatocystis is able to fix without harm a quantity of zinc equal to more than 1/1100 of its weight. Zinc is regarded as a catalytic element, as essential to the well-being of the plant as are the more obvious nutrients, carbon, sulphur, phosphorus, &c., in spite of the minute traces in which it occurs.