Studies on Fungicides — III 75 



from insoluble copper protectants is spore excretions. Various atmos- 

 pheric factors, especially meteoric waters, may be supplementary agents, 

 and perhaps also the excretions from suscept parts, though this has not 

 been clearly established. In any case, these agents appear to be non- 

 essential for protective action. In addition, various calcium compounds 

 in the case of bordeaux mixture and copper-lime dust, and probably also 

 the alkalinity of the mixture, play a role. Finally, there may be an infi- 

 nitely slight accumulation of copper from that which presumably is always 

 present in equilibrium with the most " insoluble " of copper protectants. 

 No definite conclusions can be drawn from the preliminary experiments 

 performed to study this point. 



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