ii8 PRACTICAL TREE REPAIR 



more like wood in its properties, and capable of 

 becoming more nearly like an i^itegral part of the 

 tree. The moment this need was stated, asphalt 

 suggested itself as the material which most nearly 

 meets the requirements. It is, indeed, practically 

 the only solid filling material which has been 

 brought forward as a substitute for concrete. Its 

 eminent fitness is obvious. It is slightly elastic, 

 while concrete is absolutely rigid; it is waterproof, 

 while concrete absorbs water; it adheres to 

 wood, while concrete does not; it is light and 

 warm, while concrete is heavy and cold. 



In a preceding chapter, under the topic of 

 wound dressings, some of the various kinds of 

 asphalt have been mentioned. It cannot as yet be 

 definitely stated what form of asphalt is best suited 

 to tree work. For outside waterproofing appli- 

 cations, the writer is convinced that bituminous 

 cement made from the natural asphalt is the best. 

 For cavity work it may sometimes be little more 

 than a question of choosing the cheapest material, 

 especially when the metal-front system is used. 



Such brief description as is necessary of the 

 methods of mixing the asphalt with other sub- 

 stances, in the preparation of the actual filling-ma- 

 terial, is best deferred until the processes of filling 

 appropriate to each material are being described. 



