TREE SURGERY AS A SCIENCE 



535 



ment. The causes which produce cav- 

 ities are almost innumerable, but the 

 most common are the following: im- 

 proper trimming, splitting of weak 

 crotches, gnawing by horses, bruises 

 caused by lawn mowers and other im- 

 plements, the raising of the bark by 

 lightning, and, not infrequently, the 

 lacerations caused by the climbing- 

 spurs used by telephone men, and, sad 

 to say, by the ordinary "tree-butcher." 

 It may safely be said that as long as 

 the bark, including, of course, that on 

 the roots, remains perfectly sound and 

 whole, there will be no cavities ; there- 

 fore, whenever the bark is destroyed 

 and the wood fiber is left un- 

 protected, there will be a cav- 

 ity. Fully half the work of 

 the tree surgeon is undoing 

 the damage that some one else 

 has done. One of the worst 

 troubles which he encounters 

 is the result of improper trim- 

 ming. When the average 

 man cuts otf a limb, he gen- 

 erally does so where the di- 

 ameter is the smallest, neces- 

 sarily leaving a stub ; or he 

 may leave the stub under the 

 impression that the decay will 

 be so much the slower. And 

 in those rare cases where the 

 cut is made properly, it is sel- 

 dom that he uses any precau- 

 tion to keep the wood 

 from decaying while the 

 bark is healing over the wound. 

 All cuts should be made flush 

 with the limb or trunk from which 

 the branch is taken ; but, in order to un- 

 derstand the reason for this, it is neces- 

 sary to take into consideration the cir- 

 culation of the tree, and the way in 

 which it heals. As a matter of course, 

 Avhere there are no leaves there can be 

 no circulation ; and where there is no 

 ■circulation there can be no healing. 

 Where the end of a limb is taken off, 

 the circulation is destroyed in that part 

 •of the tree, the bark dies back to the 

 main limb or trunk, and the stub de- 

 cays till it falls out and leaves a cav- 

 ity. The same thing is true when the 



top of a tree is cut back improperly. 

 The stubs invariably decay, unless the 

 cut is made down close to a good, live 

 branch, sloping away from that branch, 

 and protected by some method of water- 

 proofing. 



The method of treating a cavity, as 

 devised by Mr. Davey, is extremely 

 comprehensive. It is based on exactly 

 the same principles as those of dentis- 

 try. First of all, the decayed matter is 

 carefully removed back to good, healthy 

 tissue. The walls of the cavity are 

 then thoroughly water-proofed and 

 studded with nails driven in, which 

 serve to hold the filling firmly against 



A WATER'SHED 



Ash Tree on John D. Rockefeller Estate, Tarrytown, N, Y., showing Watcr^shed 



around Cavity 



the sides. Drain-tubes are always put 

 in at the bottom of the cavity, extend- 

 ing to the outside of the tree, so that 

 in case water gains entrance from any 

 unforeseen cause, it may be carried off, 

 and the cavity remain dry. Wherever 

 the tree is especially weak because of 

 the cavity, steel braces, both longitudi- 

 nal and transverse, are put in for the 

 purpose of reinforcement. Water- 

 sheds are invariably used, to keep the 

 moisture out ; these consist of deep 

 V-shaped grooves extending from the 

 inside of the top, along both sides of 

 the mouth of the cavity, and out at the 

 bottom, over a ledge that slopes up- 

 ward and inward. Then the filling of 



