22 TREE WOUNDS AND DISEASES 



an aged specimen. When the cavity in a 

 hollow stem is so large that a person can enter 

 it, the work of either filling with a suitable 

 composition or supporting with wooden struts 

 is greatly simplified. 



Covering holes in the trunk with wood in- 

 stead of lead or zinc has had promising results 

 in a number of old elm trees in a London park 

 that were operated upon fully a quarter of a 

 century ago. The wood used was oak and 

 Spanish chestnut, formed to exactly fit the 

 openings, and which, after being treated with 

 creosote, not only prevented the ingress of 

 water, but, in most cases, did not prevent a 

 callus forming over the blocks. Severe and 

 well-directed pruning of the head will often, 

 too, when the tree is not too far advanced in 

 decay, rally and prolong the life of an oak, an 

 ash, or a chestnut. Many examples of the 

 good effects of carefully reducing the upper 

 branches of old and weather-worn trees could 

 be pointed out. 



Recent experiments have proved the value 

 of a mixture of sawdust and asphalt for filling 

 cavities. It is particularly valuable in cases 



