STRUCTURE AND GROWTH 19 



in two through the callus a thin layer of dead or 

 dormant bark would be found beneath the callus, 

 dividing it from the surface it has spread across. 

 During the healing process we will usually dis- 

 cover that the callus grows most rapidly at the 



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Normal callus growth around Diagram of the flow of sap 

 oval wound about an oval wound 



sides of the wound, more slowly at the top of it, 

 and most slowly at the bottom. The reason for 

 this is indicated by the accompanying figure, which 

 is a diagrammatic representation of the flow of 

 sap through the cambium around a wound in the 

 trunk. The sap tends to flow in a fairly straight 

 line. The greatest flow is past the sides of the 

 wound. Less comes to the top of it, and the 



