GENERAL METHODS 129 



tern a network of strap-iron, elaborately bolted to- 

 gether, is staggered back and forth inside the tree. 

 But the reinforcing elements are so short and weak 

 in comparison with the leverage of the limbs and 

 the power of the wind, that it is difficult to believe 

 that they have any substantial strengthening value. 

 A;iother method is to reinforce the concrete with 

 rods of steel, just as structural concrete is rein- 

 forced. This can only be of value when it is used 

 in a long cavity which is decidedly more weaken- 

 ing in the middle than it is at either end. If the 

 tree is weakest at the ground this system would 

 increase the danger because it would destroy the 

 shock-absorbing capacity of the trunk and make 

 of it a lever by which the top could bear on the 

 lowest part of the trunk. Doubtless these and 

 similar systems of interior bracing have occasional 

 uses, but before going to much expense in that 

 direction it is a good idea to make a diagram of 

 the proposed reinforcements and submit it to a 

 civil or structural engineer. If his discussion of 

 the project leaves you convinced of its value, go 

 ahead. 



In the case of a tree so far gone as to suggest 

 such elaborate interior reinforcement, it will 

 usually be best to employ the " open system " of 

 cavity treatment which will be described in another 

 chapter. Strengthen the weak limbs with outside 

 braces. If possible, strengthen the whole tree by 



