40 S. E. A. McCallan 



atmosphere. The protoplasm of the spores on the film of bordeaux 

 became badly shrunken, while the spores beyond the zone of bordeaux 

 were apparently normal and many had germinated. From these results 

 Barker and Gimingham conclude (pages 88-89 of reference cited) : 



It seems reasonable to postulate, therefore, a solvent action on the part of the fungus 

 which is not powerful enough normally to produce serious toxic effect except when direct 

 contact occurs. At the same time it is evident that such action is purely local and cannot 

 result in the bringing into solution of sufficient copper to exercise a general fungicidal action 

 over the whole surface of a leaf. 



Pickering (1912) has criticized in some detail Barker and Gimingham's 

 (1911) conclusions, and points out that the majority of their experiments 

 were with the no-excess-lime bordeaux (lOCuO, SO3), which is not entirely 

 insoluble. These criticisms have been sharply refuted by Barker and 

 Gimingham (1914b). 



The later work of Barker and Gimingham (1913, 19141)) is concerned 

 chiefly with seedling root-hairs, the action of which they consider com- 

 parable to that of germinating spores. The seedlings were placed in 

 various copper-compound suspensions, chiefly no-excess-lime bordeaux. 

 Ordinary bordeaux and copper carbonate also were used. Barker and 

 Gimingham found that only when the root hairs were in contact with 

 the particles of the copper compound did injury and death result. The 

 root hairs not in contact escaped injury and grew. The injurious action 

 was entirely local, and, as the authors state (1913:61), therefore "cannot 

 be explained as a result of the production of soluble copper by atmos- 

 pheric agencies." The authors emphasize the action of the cell wall, and 

 finally conclude, in part (page 62 of reference cited) : 



(1) Living cells with readily permeable walls of the unchanged cellulose type or its equiva- 

 lent are able to produce and absorb soluble copper from insoluble compounds such as the 

 basic sulphates. 



(2) The area over which a single cell can exert the solvent action is limited by the size of 

 the cell or, perhaps, more accurately, by the quantity of the solvent diffusing from it. Groups 

 of cells acting in conjunction may cause appreciable action over a wider area than an isolated 

 cell singly. 



(3) The fate of the organism depends upon the relation between the amount of soluble 

 copper produced and absorbed and the rate of growth of the organism. 



Butler (1914:139), in view of his experiment with distilled and tap 

 water which has already been discussed under atmospheric agencies, 

 assumes that the sporangia of Phytophthora or of Plasmopara could not 

 have an excretory solvent action, "for, so far as at present known, organic 

 solvents of the copper precipitate of bordeaux mixtures are more active 

 in alkaline than in neutral mixtures, and their action is not materially 

 interfered with when tap-water is used in lieu of distilled water." 



Lutman (1916) made some interesting studies, but did not definitely 

 commit himself to any of the three hypotheses. He employed spore tests 

 using spores of Phytophthora omnivorum, Sclerotinia cinerea, and Ustilago 



