16 TREE WOUNDS AND DISEASES 



side of the living bark ; in other words, the 

 cambium should be left free for expansion. 

 Sometimes brickbats broken small are used 

 instead of gravel, but for various reasons 

 concrete is preferable. The concrete surface 

 may be prevented from cracking by applying 

 annually a coat of paint, which, for appearance 

 sake, may be of a similar colour to that of the 

 bark of the tree. This can best be undertaken 

 when the sap is not running too freely, as then 

 the cambium is less active and less liable to 

 injury. 



In the case of a large tree in which the 

 trunk is quite hollow, usually with a basal and 

 top opening, the amount of cement required 

 to fill the cavity precludes the possibility of 

 such being employed, on the score of economy ; 

 but where the hollow only extends for a com- 

 paratively short distance upwards and inwards 

 the composition is to be recommended. When 

 a large amount of material is required to fill a 

 hollow stem, clean bricks broken to about the 

 size of a golf ball may be used, but they must 

 be packed firmly, and the surface, wherever it 

 is exposed to the weather, glazed over with 



