270 PRUNING. 



living or dead, consists in cutting close to and per- 

 fectly even with the trunk. Many authorities have 

 hinted at this, the cardinal principle of all pruning ; 

 but M. de Courval first clearly demonstrated its im- 

 portance, while his discovery of the value of coal-tar, 

 or the refuse from gasworks, as a covering for wounds 

 made in pruning, renders the application of his rule in 

 all cases entirely safe. 



" It follows that a wound caused by the amputation 

 of a branch must, in order to heal properly, be made 

 perfectly even with the trunk, that every part of its 

 outer edge may be brought into direct communication 

 with the leaves through the network of cells destined 

 to convey the descending sap. Although this theory 

 rests on one of the most elementary principles of 

 vegetable physiology, it has not been applied before 

 to practical forest management. The amputation 

 having been made, even with the trunk in the manner 

 explained, new wood will soon appear, forming first 

 round the top and sides of the wound, which is soon 

 completely surrounded by the new growth ; the wound 

 is gradually healed over, and the decay of the trunk 

 prevented. The time required for the complete heal- 

 ing of a wound depends, of course, upon its dimensions 

 and the natural vigour of the tree. 



" The principle being established that large wounds 

 can be made without injury to the tree, if care is 

 taken in the manner indicated to prevent decay, it is 

 easy to show the advantage of cutting off injured 

 branches of any size. It is preferable to avoid, of 

 course, the necessity of making large wounds, by 

 properly pruning trees when young. All foresters 

 agree that trees should be trained when young ; but 

 De Courval has amply demonstrated, by numerous 



