192 SCIENCE AND FRUIT GROWING 



leaves were dipped into the mixture to be examined, the super- 

 fluous liquid shaken off from them, and then left on glass plates, 

 being kept moist by spraying with water once or twice a day. 



The scorching action was found to be so dependent on the various 

 conditions of the experiment, that determinations all made at- 

 the same time could alone be compared with each other. The 

 action was also complicated by the occurrence of what may be 

 termed natural scorching, due to the dying of the leaf, and the 

 effect of this could not always be discriminated from the effect 

 of the copper : it was insignificant in amount, however, when 

 the treatment did not extend beyond 24 hours. It was found to 

 be essential that all the leaves taken in any series should be of 

 the same age, and, of course, all sound. Differences of 60 per 

 cent, were found in the behaviour of similar leaves of different 

 ages, the younger being the more susceptible in the case of pears, 

 and the older in the case of apples ; but this reversal with apples 

 of what appears to be a general rule the greater susceptibility 

 of young leaves was due to the fact that in this case the young 

 leaves were more hairy than the old ones, and were, therefore, 

 wetted less readily : rubbing the leaf, however lightly, increased 

 the action by improving the contact with the liquid. Leaves 

 taken in July were always found, unless they were leaves of a 

 second growth, to be too much injured to yield concordant 

 results ; but one curious effect was noticed in their case, that 

 the apparent scorching effect of weak copper solutions was less 

 than that of water only. The explanation of this was, that the 

 apparent effect is the combined result of copper injury and of 

 the natural dying of the leaf; but this natural dying is not a 

 simple chemical change; it is hastened by, and is, perhaps, 

 entirely dependent on, the action of fungi, bacteria and other 

 organisms; the copper would impede the action of these, and, 

 hence, retard decay : in fact, copper is a preservative, as well 

 as a destructive agent, and is made use of in the former capacity 

 (though very improperly) for preserving vegetables. 



Leaves of apples (two varieties), pears, damsons, privet and 

 rose were examined by the immersion method in solutions of 

 the sulphate, chloride and acetate of copper containing from 

 0-32 to 0-00016 per cent, of the metal. The three salts gave 

 throughout closely similar values, the means of all the series being 

 actually identical; so that, as regards scorching, the result is 

 the same as that obtained by Clark in respect to fungicidal action, 

 namely, that the effect is independent of the nature of the copper 

 salt producing it. 



