SHADE TREES. 



185 



The blocks should be arranged in the cavity opening so that the radial 

 and tangential surfaces of the structural elements in the blocks coin- 

 cide in general with those in the tree. It is not necessary to lay the 

 blocks in cement, but in some cases painting 

 the surfaces which will come into contact 

 with one another with an elastic cement is of 

 advantage. The blocks are fastened to the 

 tree by means of special iron braces and held 

 securely by iron re-enforcements. Besides 

 being especially adapted, owing to their 

 phj'sical properties, to use in trees, such 

 blocks are durable, light and easy to fit, and 

 are better adapted to swaying movements 

 and crushing pressure found in narrow 

 cavities than rigid or less plastic substances 

 such as have been used heretofore. The 

 disagreeable and injurious effects arising 

 from bleeding may be taken care of by 

 this method of cavity treatment, and con- 

 structive work may be done in winter as 

 well as in summer. 



Fig. 57. — CroBS-section of 

 Ulustration shown in Fig. 

 56. C, cavity; B, chemi- 

 cally treated blocks; I, 

 iron re-enforcement in 

 grooves; X, longitudinal 

 section of blocks. 



Tree Guards. 



There is almost no end to the types of tree guards used to protect trees. 

 Some of these are good and others are of little value. The purpose of a 



Fig. .58. — Different types of tree guards: 1, wooden strips nailed to a tree; 2, wooden 

 strips nailed to a tree and banded with iron; 3, old type of wooden tree guard; 

 4, wooden strijis banded with iron tightly to the trunk of the tree; 5, similar to 4; 

 all objectionable types. 



tree guard is protection, and the guard should cover the tree to a height 

 of about 6| feet; it should be as light and as inconspicuous as is con- 

 sistent with strength and protection; and should allow the tree ample 



