10() INSKCTICIDES, FUNCIIC'IDI-.S, AND ^VEE]) KILLEllS. 



in the soil bear strong doses because they are there converted into in- 

 soluble salts, the roots of which only absorb small quantities incapable 

 of producing a poisonous effect. Haselhoft' and Gossel found that the 

 pi'esence of 0'235 per cent of zinc oxide in a soil does not injure vegeta- 

 tion but that zinc sulphate in the same dose calculated as oxide was 

 poisonous. 



Action of Zinc Sulphate on Cryptogamic Parasites. — Accord- 

 ing to comparative experiments by Wuthrich zinc sulphate acts like 

 green vitriol, and in the same doses as the latter destroys the spores of 

 different fungi. It is thus like green vitriol 10 times less poisonous 

 than blue vitriol and 100 times less active than mercuric chloride, 

 the three salts being used in solutions containing their chemical 

 equivalents. 



Phi/toplithora infestans, De By. — The conidia treated by a 0"0143 

 per cent solution are weakened, and after fifteen hours in a 0"143 per 

 cent solution destroyed. The zoospores of this fungus are stunned in 

 a minute in a 143 per cent solution and killed in fifteen hours. 



Peronospora viticola, De By. — The conidia are weakened by a 

 0-00143 per cent solution. Their growth is stopped by 0-0143 per cent 

 solution. 



Puccinia graminis. — The uredospores and the tecidospores are 

 arrested in their growth by the action of a 0-143 per cent solution. 



Ustilago Carho (smut). — The growth of the conidia is retarded by 

 a 0-143 per cent solution, but they are not killed by a 1-430 per cent 

 solution. According to Madame de Ponsard, spores immersed for four 

 hours in a 1 per cent solution partially germinated. 



Claviceps purpurea, Tul. (ergot). — The conidia are not killed by a 

 1-43 per cent solution. 



Use. — Peronospora viticola, De By. (mildew of the vine). — Follow- 

 ing experiments by Wuthrich who showed that the action of zinc 

 sulphate on the spores of this fungi is evident though comparatively 

 weak, Guocdenovic made experiments with a 1-0-1-5 pei' cent zinc 

 carbonate with a bouillie made by mixing solutions of zinc sulphate and 

 sodium carbonate. The results were not comparable with those ob- 

 tained by the Burgundy bouillie nor the bouillie bordelaise. Passerini's 

 experiments also showed that a bouillie with a zinc sulphate basis had 

 no curative action, like copper bouillies. 



Ustilago. — Advised by Mine, de Ponsard in 1 per cent doses for dis- 

 infecting seed-corn, zinc sulphate did not give the results expected. 

 Loverdo regards its prophylactic action as doubtful and inefficient. 

 He regards the salt as unfit to replace copper salts. 



Pkijlloxera rastatrix, Planch. — Mouillefeit completely destroyed 

 the phylloxeras on an infested root by steeping it in a 1 per cent solu- 

 tion of zinc sulphate. 



6o. Borate of Zinc, ZnBP-. — Preparation. — By precipitating 

 a solution of zinc sulphate by [a solution of] borax. On mixing the 

 concentrated solutions a gelatinous precipitate is obtained. 



Use. — Galloway examined on rust the effects of a bouillie made by 

 precipitating 133 grammes of zinc sulphate by a concentrated solution 

 of 133 grammes of borax and making the whole up to 15 litres. Oats 



