THE WOUND DISEASES 91 



is a mechanical injury as truly as the mark of 

 the whiffle- tree or of the wind. If this exposed 

 surface is not cared for, it may prove an inlet 

 for disease and decay. Unfortunately, this 

 matter has not received adequate attention from 

 mycologists studying wound-rot fungi ; and all 

 that we can do at this place is to suggest in a 

 general way what may take place, especially in 

 the larger wounds. It is not to be understood 

 that all neglected wounds lead to wound -rot dis- 

 eases ; but the point is that they may induce 

 such diseases, since a certain amount of death 

 and decay are inevitable ; and the larger the 

 wound, the greater the danger. 



"First, then, we are concerned with the condi- 

 tions which bring about and encourage this rot- 

 ting. It is well known that when only the corky 

 outer layer of bark is removed, another corky 

 layer is readily formed for needed protection ; 

 but when a branch is sawn across, as in prun- 

 ing, the wood elements are directly exposed to 

 the air. It is then impossible for a corky layer 

 to be formed, and it may be several years before 

 a callus will inclose the exposed part. The sap- 

 wood of this exposed area soon loses connection 

 with the active functions of the plant, and .dies. 

 All heart wood is inactive, but in sound trees it 

 is thoroughly protected from the air, while the 

 exposed scar left by the pruning saw is open to 

 weather. The open tubes which make up the 



