208 INSECTICIDES, FUXGICIDES, AKD WEED KILLEES. 



plants ; stimulating in small doses blue vitriol is poisonous in large 

 doses. It is to be remarked that blue vitriol shares this stimulating 

 action on alga? with many other poisonous salts. Eaulin remarked in 

 1869 that zinc and silicium salts increased the vitality of the fungus 

 Aspergillus niger. Niigeli, Pfeffer, and Eichards made the same- 

 remark on zinc, nickel, and cobalt salts, used on the fungus Aspergillus 

 niger and Penicillium glaucum, and on the algae Protococcus, Chroo- 

 coccus, Stigeodonium, and Honnidium. The vitality of fungi and alga 

 is, to sum up, stimulated by the sulphates of zinc, nickel, cobalt, iron, 

 and copper, mercuric chloride, sodium fluoride, lithium nitrate, potassium 

 arseniate. The right dose for alga^. is smaller than for fungi. For 

 blue vitriol the maximum dose is 0"012 per cent; for mercuric chloiride 

 O'OOIS per cent. Ferments (leavens) behave in the same way as fungi. 

 According to Kruger the alcoholic fermentation of wort by Saccha- 

 romyces ellijjsoides is favoured by doses of blue vitriol smaller than 

 0'01856 per cent. Pichi and Eommier found that a solution contain- 

 ing O'Olo per cent of blue vitriol began to impede fermentation and 

 that 0-03 per cent reduced it perceptibly. Besides copper salts are 

 precipitated by fermentation, the ferments can thus find in the lees 

 the amount of copper favourable to their development (Biernacki and 

 Kruger). There are, however, exceptions amongst plants. Thus the 

 fresh-water algge spirogyra dies in a solution containing only 0-000001 

 per cent of blue vitriol (Niigeli), whilst other algge resist solutions of 

 0-012 per cent perfectly. Penicillium glaucum would even be capable 

 of growing in a concentrated solution of green vitriol. This fact, 

 remarked by Trabut, was examined by De Seyes. In a nutritive solution 

 blue vitriol does not disturb the growth of Penicillium glaucum (Trab.) 

 in a 9-5 per cent dose. This fact must, however, be considered in 

 another light to understand it. It is, in fact, recognized that Peni- 

 cillium glaucum can grow in a poisonous medium without feeding on 

 its elements, but by using the medium solely as a support. Hence this 

 mould is perfectly capable of growing on a crystal of nitrate of silver, 

 or in a solution of 1 per cent of corrosive sublimate. Whilst germin- 

 ating spores of Penicillium glaucum in a 9-5 per cent solution of blue 

 vitriol, De Seyes observed that growth did not occur except on the 

 edge of the vessel, where the water of condensation was accumulated. 

 Saccardo stopped all growth of this fungi in a medium containing 

 5 per cent of blue vitriol by agitating the solution ; whilst at rest 

 gi'owth was so normal that it formed conidicB. Penicillium therefore 

 does not possess a special immunity for copper salts, as had been 

 imagined, but behaves like other fungi, and E. Otto gives the dose of 

 0-008 per cent as favouring its development. This dose is hardly 

 greater than that required by Aspergillus niger, 0-004 per cent. 



Action of Blue Vitriol on Parasitic Fungi. — Benedikt Prevost,^ 

 in 1807, discovered the poisonous action of blue vitriol on parasitic 

 fungi. In his experiments to determine the action of boiling water 

 on spores, he made the sensible remark that water boiled in a copper 

 vessel alone had the power to prevent spores from germinating. He 

 then determined that it sufficed for the water to contain 1 part in 

 400,000 of its weight of blue vitriol to prevent the spores of rust from 



