134 PRACTICAL TREE REPAIR 



at first glance they may seem of slight importance, 

 are not so much differences of method as they are 

 differences of purpose. In other words, the men 

 who have developed the different systems, have 

 had different ideas as to the function of cement 

 fillings. In the early days of cement work in 

 trees, it seems to have been taken for granted that 

 the main value of the filling lay in Its strengthen- 

 ing effect. The question of how this supposed 

 effect was brought about does not seem to have 

 been asked. It simply " seemed natural " that a 

 tree which was full of hard cement should be 

 stronger than a hollow tree. However, when 

 irregular cracks appeared across the face of every 

 large cement filli;ig, and when the filled trees 

 proved to be no more resistant to storms, appar- 

 ently, than unfilled trees, tree-men began to ask 

 themselves whether they were working on the 

 right principle. The idea that the cement was 

 of considerable strengthening value was not 

 abandoned, however, and the difficulties which had 

 developed were explained as being due to the 

 absence of a sufficiently close bond between the 

 concrete and the wood. The most obvious 

 remedy for the trouble was to drive a lot of nails 

 into the Inner surface of the cavity. But the 

 cracks still appeared. Continuing the same line 

 of attack, an elaborate system of interior bracing 

 or reinforcing was developed. This was an im- 



