1905.] Copper Sulphate Solutions on Plants 415 



the leaves against the effects of excessive sunshine might be 

 advantageous, and Heir Schander suggests that the strength 

 of the Bordeaux mixture might be regulated according to 

 the character of the season ; thus in a hot, dry summer a high 

 percentage solution might be employed, while in a wet, dull year 

 a 1 per cent, solution could be applied, which would still be 

 sufficiently strong to destroy fungi. 



There is one other point of considerable practical interest 

 which is dealt with in this paper, and that is the cause of the 

 occasional injury to leaves and fruit caused by copper solutions. 

 Whilst observation has shown that this injury most frequently 

 occurs with solutions containing too little lime, it may also 

 happen when an excess of lime has been used ; the leaves of 

 some plants are more easily affected than others, while the in- 

 jurious effects appear to occur very irregularly and more in one 

 year than another. 



It would seem that lime is able to restrain, but not entirely to 

 prevent, the injurious effect of the copper sulphate, and that the 

 effect is more or less dependent on meteorological conditions, 

 many cases of injury, for instance, occurring in the wet summer 

 of 1902. In the case of peach leaves and apples, it would seem 

 that the addition of quicklime in excess is by no means com- 

 pletely able to prevent injury, and against a too great excess 

 of lime it must be remembered that the adhesibility of the solu- 

 tion to the leaves is thereby much diminished, whereas, so far as 

 our knowledge goes at present, a solution is the more valuable the 

 better and the longer it adheres to the leaf. 



Moreover, the fungicidal effect of the solution depends simply 

 and solely on its content of copper hydrate, and it operates only 

 so long as it exists actually as a coating on the leaf. A too great 

 excess of lime is necessarily associated with a reduction in the 

 percentage of copper hydrate in the solution, so that its fungi- 

 cidal effect is diminished. Thus we have no means entirely to 

 prevent its virulent action, particularly in the case of peach 

 and certain apple trees. Herr Schander's view is that peach 

 trees should, if possible, not be sprayed at all — at any rate, 

 never during rainy weather. If, however, it be done, it is 

 imperative to use two parts of quicklime to one of copper 

 sulphate. 



