206 TREE WOUNDS AND DISEASES 



size of a walnut, are valuable for filling hollow 

 stems or " chimney " openings where the price 

 of concrete filling would be prohibitive. The 

 surface should be covered with concrete. It 

 cannot be claimed for such a filling that it 

 strengthens the hollow branch or trunk as 

 concrete would, but in exceptional cases, and 

 where the apertures are large, broken bricks 

 make an excellent substitute, and the cost is 

 nil. Breeze or cinders are also used for mixing 

 with the cement, but they are porous and admit 

 damp. 



Asphalt. This has several points of re- 

 commendation, though its use may be said to 

 be but imperfectly recognised. First of all, 

 owing to its comparative elasticity, it slightly 

 yields to the motion of the tree, while it is 

 readily applied and is absolutely waterproof. 

 So far, we have little experience of asphalt as a 

 filling material for hollow stems and branches ; 

 but experiments in hand in various parts of 

 London lead us to believe that it will in the 

 future supersede concrete for that purpose. 

 The cost, too, is not prohibitive. 



Sawdust and Asphalt. Where concrete is 



