154 SCIENCE AND FRUIT GROWING 



However satisfactory undiluted paraffin might be as an in- 

 secticide, its action on the trees had to be considered. To 

 examine this, a number of apple trees were painted with 

 various oils on dates between March 10 and April 3. In all 

 cases much damage was done, extending from the destruction 

 of the fruit buds to the injury of shoots; and the damage 

 was on the whole greater, the less volatile the oil. With the 

 lighter oils, though the fruit buds were injured, the wood of the 

 tree and the growth buds did not seem to have been much 

 affected, and, consequently, considerable growth followed the 

 treatment, though it did not start till a late date. The weather 

 conditions cloudy or clear at the time of applying the oil, 

 did not have any appreciable effect on the results, as they are 

 sometimes stated to have, the mortality of the fruit buds being 

 89 per cent, with cloudy weather, and 91 per cent, with clear 

 weather; but warm, windy conditions following the application, 

 reduced the damage by hastening the evaporation of the oil, 

 and hence a later date for such treatment would generally be 

 preferable to an earlier one. It was very noticeable that, for 

 weeks after the application of the paraffin, the trees were con- 

 tinually wet, drops of water often hanging on the branches; 

 evidently, when any moisture had been deposited on the tree, 

 the paraffin left on the bark had spread over it, and prevented 

 its evaporation. This condition of continual wetness would, no 

 doubt, be sufficient in itself to account for much of the injury 

 (VI, 135). 



The effect of dipping young trees in oil was also examined, as a 

 consequence of its having been found that undiluted paraffin was 

 one of the most effective remedies for woolly aphis. Some stocks 

 affected with this pest, had been worked, and were subsequently 

 lifted, and dipped bodily into paraffin, being left in it for five 

 minutes, and then exposed for another thirty minutes before 

 being replanted. Where the oil used was the less volatile solar 

 distillate, all the trees were killed; where it was lighting oil, 

 two-thirds of the scions and 8 per cent, of the stocks were 

 killed; but where petrol was used, the mortality of the scions 

 was only 10 per cent., and the surviving trees showed in the 

 succeeding year a vigour of growth as good as that of the untreated 

 trees. Such treatment proved to be quite fatal to the aphis 

 (p. 220), and, therefore, taking care to use petrol, may be 

 safely and effectively applied to nursery stock (X, 7). 



In view of the disastrous effect of spraying fruit trees with 

 paraffin oil, even when the trees are in the dormant condition, 



