B. T. 1'. BaRKKR AM) (\ 'W (^IMINGHAM 15 



accounted for bv lou^li weather causing daniafio to the foliage, or by a 

 serious insect attack. Again the general opinion of practical men^ that 

 the severity of Bordeaux injury is determined by the weather condi- 

 tions at the time of spraying and that the injury is most serious when 

 rain immediately follows the spraying fits in well with the view here 

 suggested, since in wet weather any injuries present will heal over much 

 less quickly and will therefore be capable of dissolving copper during 

 a longer period. 



In view of these considerations as to the important part played by 

 im juries to the leaf surface in determining the extent of Bordeaux 

 scorching, it becomes interesting to enquire whether the presence of 

 such injuries is the sole cause or whether Bordeaux mixture does ever 

 cause scorching on undamaged leaves. This is not an easy point to settle 

 satisfactorily. It appears that, as recorded above, there is no notice- 

 able scorching of foliage which has been carefully protected ; and indeed 

 we have a good deal of evidence emphasising the impenetrability of 

 the undamaged leaf cuticle of ordinary healthy summer foliage. For 

 example, the general surface of healthy leaves stands immersion in 

 5 % or even 10 % copper sulphate solution remarkably well ; and on 

 repeating many of the experiments with damaged and undamaged 

 foliage described above, but using 5 % copper sulphate solution in place 

 of the Bordeaux mixture, almost identical results were obtained. The 

 damaged leaves indeed " scorched " worse with copper sulphate than 

 with the Bordeaux mixture, but the undamaged leaves remained 

 almost entirely unaffected, unless the time of contact was very pro- 

 longed. 



The general conclusion which may be drawn from a large number 

 of experiments on the effects of solution of copper sulphate upon the 

 foliage of different varieties of apple is that, except where the leaves 

 are originally damaged in some way, a short time of contact with a weak 

 solution causes little or no immediate injury, though a longer time of 

 contact may initiate injury to the under surface^. Even, however, 



1 Confirmed experimentally by Crandall (loc. cit.) and by Hedrick (Ncu- York Agric. 

 Expt. Sta. Bull. 287). 



" It is somewhat difficult to understand exactly what is the position taken by Crandall 

 with regard to this point. On p. 232 of his Bulletin, after describing some experiments, 

 he concludes that " tlie uninjured epidermis of apple leaves was not permeable bv copper 

 sulphate solutions" : whilst his conclusion No. 16 runs " . . . . burning quickly follows appli- 

 cations of copper sulphate even when the solutions are very dilute." Possibly the latter 

 statement refers only to damaged foliage, in which case his observations are in full agree- 

 ment with those here recorded. 



