22 OF TIJE BARK. 



we find in appropriate vessels the resin of the Fir and 

 Juniper, the astringent principle of the Oak and Wil- 

 low, on which their tanning property depends, the fine 

 and valuable bitter of the Peruvian Bark, and the ex- 

 quisitely aromatic oil of the Cinnamon. The same 

 secretions do indeed, more or less, pervade the wood 

 and other parts of these plants, but usually in a less 

 concentrated form. 



When a portion of the bark of a tree is removed, 

 the remainder has a power of extending itself laterally, 

 though very gradually, till the wound is closed. This 

 is accomplished 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 protected from the injuries of the atmo- 

 sphere, 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 ad- 

 vantage by the late Mr. Forsyth of Kensington gar- 

 dens, the history of whose experiments is before the 



