74 S. E. A. McCallan 



lime dust. When air was forcibly drawn through the distilled water which 

 had stood on the bordeaux mixture (dried) or the copper-lime dust for 

 periods of 5 to 9 days, the resulting filtrates were rendered only slightly 

 toxic. If rain water, which exhibits greater solvent action, was substituted, 

 the filtrates were more toxic. However, rain water in itself does not allow 

 quite as good germination of the spores of Sclerotina americana as does 

 distilled water. The action of atmospheric agencies in rendering copper 

 soluble from insoluble protectants seems to be relatively unimportant. 



7. The filtrate from water in which spores of Sclerotinia americana had 

 germinated, when placed on bordeaux mixture (dried) or copper-lime 

 dust for 2 days, invariably rendered the filtrate from the resulting suspen- 

 sion toxic. The filtrate from suspensions of germinating spores was non- 

 toxic. The control solutions — that is, the filtrates from pure water 

 which had stood on the protectant — always gave a high percentage of 

 germination. This seems to demonstrate the excretion of a solvent agent 

 by the germinating spores. 



8. Bordeaux mixture placed in collodion sacs of a certain degree of 

 porosity, and the whole placed in distilled water, did not appear to give 

 a diffusible soluble copper, since the outside water was non-toxic to the 

 spores when the sacs were removed. If, however, spores were placed in 

 the water in the presence of the bordeaux-containing sacs, they did not 

 germinate, thus indicating the production by the spores of some solvent 

 agent capable of diffusing through the dialyzing membrane to free diffusible 

 copper. 



9. In all the experiments performed, the copper protectants were defi- 

 nitely toxic only in those cases in which the spores, or filtrates from suspen- 

 sions of germinating spores, were able to maintain an aqueous connection 

 with the protectant. Spores placed at varying distances from a drop of 

 dried bordeaux mixture, and connected therewith by a bridge or film of 

 water, were entirely inhibited from germinating at a distance of 7.5 milli- 

 meters. As the distance of the spore from the bordeaux increased, the 

 percentage germination of the spores also increased. This clearly demon- 

 strates that direct contact is not essential for toxic action by bordeaux 

 mixture or copper-lime dust. 



10. No definite evidence could be obtained, either in favor of or against 

 the cumulative-action hypothesis — that is, the accumulation of copper, 

 by the spores, from the very minutes traces presumably present in solution 

 in equilibrium with the " insoluble " copper protectant. 



11. Preliminary tests seemed to indicate that the spore excretions of 

 Sclerotinia americana were very slightly acid, to the extent of about the 

 equivalent of N/20,000 HC1. 



12. All the evidence obtained in this investigation appears to demon- 

 strate that the chief agency in bringing about the liberation of copper 



