STRUCTURE AND GROWTH 17 



of it. Insomuch as the main current of sap is 

 from the leaves to the roots (and in spring 

 from the roots to the young growing twigs, for 

 the sap which supplies them with the materials of 

 growth is mostly stored over winter in the roots), 

 it is obvious that cambium that lies in this circuit 

 will be best nourished and grow fastest, and that 

 patches of cambium which for any reason lie 

 aside from the main thoroughfares of sap circula- 

 tion will receive least sap and will produce the 

 least growth, and that patches which are com- 

 pletely isolated will of necessity die. These facts 

 govern the making of incisions and the healing of 

 wounds in trees. 



A careful study of the healing of wounds is an 

 excellent preparation for making incisions, which 

 are only purposive wounds. 



Suppose we cut a small limb from a tree, fol- 

 lowing the practice of good pruners by making 

 the cut very close to the trunk. The result will 

 be an oval or egg-shaped wound with the cambium 

 of the trunk showing near its outer edge. The 

 sap in the cambium tends to flow in the direction 

 of established paths and in the direction of 

 least pressure. The exposed cambium around 

 the edge of the cut being such an area, it will re- 

 ceive a large flow of sap. The unconfined cells 

 will multiply rapidly. As a result of this rapid 

 growth a fold or lip will be thrown out from the 



