No. 4.] 



TREE SURGERY. 



443 



Fig. 1. — Woiind made by removing a 

 large branch fi-om a tree trunk. This 

 wound is healing fi-om the sides. 



the sense that a flesh wound heals. When the limb is cut 

 off, its base remains a dead stump on the trunk, awaiting 

 the action of decay to destroy it. Here, then, is the first 

 and chief danger to which 

 the tree is exposed by prun- 

 ing. Every wound made by 

 cutting off a branch or limb 

 exposes the trunk to the 

 danger of decay. 



Now, if this dead stump 

 can be hermetically sealed 

 up, and covered over with 

 live, sound wood and bark 

 before it has begun to decay, 

 the chief danger arising from 

 its exposm'e will have been 

 averted ; and this is just 

 what, under favorable conditions, the tree normally does. 

 If the wound is made in winter or spring, no progress in 

 covering it can be made by the tree until the elaborated sap 

 returns in the following summer. Around the edges of a 

 properly made wound the wood-forming material finds no 

 impediment to its flow. As the pres- 

 sure of the bark upon the sides of the 

 wound has been somewhat lessened bv 

 cutting away the limb and by the sub- 

 sequent drying out of the wood and 

 bark, where the cut surface of each is 

 exposed to the weather, the new wood 

 and bark roll out over the surface of 

 the wound in a mass, which we call 

 the callus. 



Wounds that are elongated verti- 

 cally usually begin healing first from 

 the sides, as seen in Fig. 1, the pres- 

 sure of the bark on the cambium in 

 such cases being much less at the sides than at the top or 

 bottom. The callus usually forms at the top before it ap- 

 pears at the bottom, so that many wounds begin healing as 



Fig. 2. — Branch wound 

 healing from top and sides. 



