VARIOUS TYPES OF CAVITIES 171 



doubly difficult to keep the filling water-tight. 

 The wood on the upper side of limbs, also, grows 

 much more slowly than that on the under side, 

 and calluses are formed with equal slowness. Sad- 

 dles, therefore, are likely to be healed over very 

 slowly, so that though good work is especially 

 difficult, it is also especially necessary. 



The solution lies in correct bracing, correct fill- 

 ing, and correct dressing of the surface of the 

 filling. 



In bracing the first thing to be done is to put 

 in a brace up above from one limb to another or 

 from the trunk to the weak 

 limb, in such a way as to 

 take most of the strain off 

 the base of the limb. Then 

 bolts must be run through 

 the saddle or just below it, 

 in order to minimize the 

 amount the mouth of the 

 cavity will open and shut in tr ^ ollow splil 



during a high wind. It 



may be that some short pieces of gas-pipe or of 

 hard wood can be fixed in the cavity, pried in in 

 such a way as to make the walls as nearly rigid 

 as possible. 



Cement should never be used in filling a saddle 

 cavity. If the tree is not worth a filling of asphalt 

 the cavity should be left unfilled. 



