38 S. E. A. M<< "ai.lan 



such as those of Rhizopus and Oedocephalum, are more quickly killed 

 than thicker-walled ones such as those of Aspergillus and Penicillium. 

 Clark (1902:43) concludes: 



1. The solution of thai pari of the Ou(OII) 2 of bordeaux mixture which under orchard 

 conditions is <>f fioiqicidul vihic, is chiefly accomplished by Hn sohn nt action of the fungus spores 

 themselves, for they have power to dissolve sufficient copper to kill themselves. 



2. The amount of copper necessary for the destruction of the spores of parasitic fungi is 

 probably not more than one part of soluble metallic copper to 80,000 parts wafer (dew I. 



This work was rather severely criticized by Bedford and Pickering (1910: 

 108-109), who, in addition, showed that copper hydroxide is slightly 

 soluble (0.00012 per cent soluble copper) in water exposed to the air. 



Schander (1904) made tests in which bordeaux mixture was sprayed 

 on various kinds of leaves exposed to the rains and dews, and the filtrates 

 from these were tested for soluble copper. Schander (1904:526) con- 

 cludes (translation of original): " Upon the grounds of my experiments 

 I do not believe that enough soluble copper compounds form upon the 

 leaf to kill the spores of fungi, but I assume with Clark that, on the whole, 

 fungi dissolve enough copper from the precipitate of bordeaux mixture 

 adhering to the leaf to kill themselves." 



Ruhland (1903), studying fungicidal action in bordeaux mixture and 

 other basic coppers, concludes that the roles of atmospheric agencies and 

 plant excretions are practically negligible, but that (translation of original) 

 " in fact the spore excretes substances which bring the Cu(OH) 2 into 

 solution. The copper dissolved by the excretion which has its origin 

 in the metabolic activities preparatory to germination now penetrates 

 the spores" (page 199 of reference cited). The conclusion "that the libera- 

 tion of the toxic quantity of copper is brought about through the excreted 

 metabolic products of the pre-germination activities of the spore " (page 

 191 of reference), is based primarily on experiments in which germination 

 tests were made with spores of Aspergillus niger, Botrytis vulgaris, 

 Ciasterosporium, and Cephalothecium roseum, in (1) the control, a 0.3- 

 per-cent glucose solution, (2) the filtrate from a 24-hours-old suspension 

 of Cu(OH) 2 in a 0.3-per-cent glucose solution, (3) the filtrate from a 24- 

 hours-old suspension of Cu(OH) 2 in a 0.3-per-cent glucose solution in 

 rain water, and (4) a 0.3-per-cent glucose solution containing a suspension 

 of Cu(OH) 2 and many spores. Though not definitely stated, the water 

 in (1) and (2) presumably was not rain water. After standing thus for 

 48 hours, the results were, for all four fungi, 100 per cent germination in 

 (1) and (2), and from about 50 to 100 per cent germination in (3). How- 

 ever, Ruhland states that in (3), 100 per cent germination would result if 

 the spores were left for three days. None of the fungi germinated in (4). 

 In the case of (4), soluble copper could be detected in the filtrates by 

 testing with concentrated sulfuric acid and potassium bromide. Ap- 



