TREE REPAIR 



169 



tree and notes how this tissue be- 

 comes affected by such injuries. 



This Hving or active tissue is 

 known as the '' cambium layer," 

 and is a thin tissue situated 

 immediately under the bark. 

 It must completely envelop the 

 stem, root and branches of the 

 trees. The outer bark is a 

 protective covering to this liv- 

 ing layer, while the entire inte- 

 rior wood tissue chiefly serves 

 as a skeleton or support for 

 the tree. The cambium layer 

 is the real, active part of the 

 tree. It is the part which 

 transmits the sap from the base 

 of the tree to its crown; it is 

 the part which causes the tree 

 to grow by the formation of new 

 cells, piled up in the form of 

 rings around the heart of the 

 tree; and it is also the part 

 which prevents the entrance of 

 insects and disease to the inner 

 wood. From this it is quite 

 evident that any injury to the 

 bark, and consequently to this 

 cambium layer alongside of it, 



will not only cut off a portion of the sap supply and 

 hinder the growth of the tree to an extent proportional 

 to the size of the wound, but will also expose the inner wood 

 to the action of decay. The wound may, at first, appear 



Fig. 116. — A Surface Wound 

 Properly Freed from De- 

 cayed Wood and Covered 

 with Coal Tar. 



