188 SCIENCE AND FRUIT GROWING 



where acids were present, such as in that of leaves of the nettle, 

 no excretion of acid occurred unless the leaf was injured. But, 

 besides acids, various organic substances are capable of dissolving 

 copper carbonate, and decoctions made from the leaves of the 

 apple, pear and damson were all found to do so to a notable 

 extent. Leaves which had been injured in any way those 

 which had become scorched by atmospheric agency, or had been 

 attacked by mildew showed a like solvent action ; 1 but none 

 whatever was shown by perfectly sound leaves. Leaves of the 

 lime, horse-chestnut, etc., which naturally excrete liquids, were 

 found to dissolve copper, even when uninjured. 



Though mildewed apple twigs dissolved copper, the spores of 

 the mildew, when separated from the twigs, were found to be 

 quite incapable of doing so, and all the experiments which have 

 been adduced in favour of the view that the copper is dissolved by 

 excretions from the fungus really afford no evidence on the point, 

 for precisely the same results may be obtained by substituting 

 for the fungus, a piece of iron or some potassium ferrocyanide, 

 neither of which give off solvent excretions, but which, however, 

 show that dissolved copper is present (XI, in ; XIV, App. 276). 

 That fungicidal action may be exhibited by Bordeaux mixture while 

 it is still alkaline is equally inconclusive, for the basic sulphates 

 of copper will act on iron while the liquid is alkaline, so long 

 as any of the compound ioCuO,SO 3 is present (XIV, App. 277 ; 

 Chem. Soc. Trans. 98, 1851) ; added to which, lime itself possesses 

 a certain fungicidal action (p. I94 2 ). 



The entry of copper into the leaf of a tree is easier of investiga- 

 tion than its entry into a fungus spore, and a considerable amount 

 of literature exists on the subject, from the work of Millardet 

 and Gayon in 1887 (loc. cit.) onwards. To the conclusions of 

 these workers it was objected that their results were obtained by 

 using copper solutions much stronger than those which would 

 be present in any spraying material, but the results at Woburn 

 (XI, 113) showed that absorption occurred, and occurred rapidly, 

 even from the weakest solutions : sound apple leaves immersed 

 in a solution containing o-ooi per cent, of copper, reduced the 

 strength of the solution to 0-0007 P er cent, in 24 hours, and to 

 0-0004 P er cent, in three days. A highly suggestive observation 

 was made in connection with this experiment, namely, that the 

 entry of copper into the leaf was accompanied by the exodus of 



1 Explaining the presence of dissolved copper in the drip-water from 

 trees sprayed with Bordeaux mixture, noticed by Crandall (Bulletin 135, 

 Illinois Agric. Exp. Station, 1810). 



2 See also, Freeman, Journ. Agric. Science, III. 400. 



