Studies on Fungicides — III 35 



experiments relative to the solvent excretion from leaves. He found that 

 the gum secretion from peach leaves did not increase the injury. By the 

 use of blue litmus solution no acid excretion could be demonstrated from 

 the leaves. Peach leaves, paraffined glass slides, and plain glass slides 

 were spra} r ed with copper hydroxide, and were then placed in the sunlight 

 and the water allowed to evaporate. Following this, the surfaces were 

 kept continuously wet with distilled water for several hours. This water 

 from the treated surfaces was then filtered, and tests were made with colls 

 of Spirogyra to detect soluble copper. The percentages of cells killed were, 

 respectively, 88, 24, and 51, from which Bain (1902:93) concluded that 

 " there is something escaping from the peach leaf which has a solvent action 

 on copper hydroxide." Bain did not, however, give the percentages of 

 cells killed in his controls, and in a preliminary experiment he found that 

 the filtrate from a stock suspension of copper hydroxide was equally as 

 toxic as that from the sprayed peach leaves. He assumes, in common with 

 the earlier workers, that the copper of bordeaux mixture exists in the form 

 of copper hydroxide. 



Schander (1904), also studing bordeaux injury, discovered that the leaves 

 of Fuchsia and Oenothera excrete acids which apparently can dissolve 

 small amounts of copper hydroxide. In the case of Phaseolus multiflorus, 

 the leaf excretions reacted alkaline and Schander was unable to demon- 

 strate a solvent action. 



Ruhland (1903), as a result of his investigations, was unable to sub- 

 stantiate the hypothesis of suscept excretions. Studying those plants 

 especially susceptible to bordeaux injury, he found that various organic 

 salts, especially malic acid and potassium, were exuded through healthy 

 uninjured leaves and fruits. However, none of these substances was ca- 

 pable of dissolving any more than insignificant amounts of basic copper. 

 In fact, similar traces of copper were dissolved by pure water containing 

 carbon dioxide, and by water from the surfaces of corked-over organs, such 

 as twigs, which did not exude any such substances. Ruhland was unable 

 to demonstrate the presence of exuded sugar. He therefore concludes that 

 the traces of soluble copper on the leaves are brought into solution by rain 

 water containing carbon dioxide and other substances from the air. 



( randall ( 1909) states that he was unable to obtain any evidence that 

 the solution of copper occurs through the agency of leaf secretions. No 

 direct experiments are mentioned. 



Bedford and Pickering (1910:109-112) planned experiments in which 

 leaves of apple, pear, and damson plums were placed in suspensions of 

 copper carbonate and copper oxide. The leaves were later removed and 

 bests were made for the presence of soluble copper. Solutions in which 

 leaves, apparently uninjured, had been placed, showed the same small 

 quantity (0.00001 per cent to 0.00002 per cent) of soluble copper as did 



