Effect of Zinc Compounds 49 



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 ziac 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 ziac 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 Sterigmato- 

 cystis in 



(a) normal Raulin's solution with ziac, 

 (6) Raulin's solution without zinc. 



The ratio of crops ajb varied fi:om 2'3 — 3"1 in four experiments, vindi- 

 cating 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 eleme^t, as essential to the well-being of the plant as are the 

 more obvious nutrients, carbon, sulphur, phosphorus, &c., ia spite of the 

 minute traces in which it occurs. 



B. 4 



