28 OF THE BABK. 



more or less, pervade the wood and other parts 

 of these plants, but usually in a less concen- 

 trated form. 



When a portion of the bark of a tree is 

 removed, the remainder has a power of ex- 

 tending itself laterally, though very gradu- 

 ally, till the wound is closed. This is accom- 

 plished by each new layer, added to the 

 bark internally, spreading a little beyond the 

 edge of the preceding layer. The operation 

 of closing the wound goes on the more slowly, 

 as the wood underneath, from exposure to 

 the air, has become dead, and frequently 

 rotten, proving an incumbrance, which though 

 the living principle cannot in this instance free 

 itself from, it has no power of turning to any 

 good account. If, however, this dead wood 

 be carefully removed, and the wound pro- 

 tected from the injuries of the atmosphere, 

 the new bark is found to spread much more 

 rapidly ; and as every new layer of bark forms, 

 as will be proved in the next chapter, a new 

 layer of wood, the whole cavity, whatever it 

 may be, is in process of time filled up. 



This operation of Nature was turned to 

 great advantage by the late Mr. Forsyth of 



