70 



S. E. A. McCallan 



TABLE 18. Percentage Germination of Solerotinia americana Conidia in Flowing 

 Water Which Had Previously Been Dripped over Copper Protectants 



Fungicide 



Apparatus control 



Water dripped over germinating spores 



Water dripped over fungicide 



Water dripped over germinating spores, then over furgicide 

 Control (usual) 



Experiment no. 



Woburr. 

 bordeaux 



Bordeaux 

 4-4-50 



Copper- 

 lime 



Per cent and type of germination 



78.7 B- 

 61.6 B- 

 17.2 D 







97.8 A 



Discussion. No conclusions can be drawn from these experiments 

 because of the instability of the fungicides, which introduced new and 

 unknown toxic favors. With the copper-lime dust there is slight evidence 

 of a solvent action on the part of the germinating spores. 



The rate of solution of soluble and "insoluble " copper compounds 



Hypothesis. If suspensions of soluble and " insoluble " copper com- 

 pounds are prepared in various dilutions in a parallel series, the soluble 

 copper compounds should be immediately toxic to the extent of their 

 total copper content. On the other hand, according to the cumulative- 

 action hypothesis only a very small trace of the " insoluble " copper com- 

 pound is at any one time in solution. It is only after a period of time 

 that an appreciable amount of the copper can be brought into solution, 

 and this is dependent on some reactive body being present to remove it 

 as fast as it comes into solution. Presumably, complete solution and 

 removal of all the copper from the " insoluble " compound would require 

 considerable, if not almost infinite, time. Therefore, with two dilutions 

 of the same total copper content, that of the soluble copper compound 

 should be very much more toxic than that of the " insoluble " compound, 

 for with the latter a period of time must elapse before any appreciable 

 percentage of the total copper can have come into solution. If, however, 

 spore-excretion solvents are active, there should be little difference in 

 toxicity, though probably the soluble compound would be somewhat 

 more toxic because of its immediate action. 



Experiments. Dilute solutions of copper sulfate were prepared. Sus- 

 pensions of an " insoluble " proprietary copper dust, of equal total copper 

 content, were likewise prepared. Spores of Sclerotinia americana were 

 added to these solutions and suspensions, and germination tests were 

 made. The recorded germinations are shown in table 19. 



