274 PHYSIOLOGY OF TREES. 



To shew that the cambium is a separate and 

 distinct organ from the alburnum of last year 

 (except by the insulated attachments before de- 

 scribed), we may only instance how completely 

 the former separates from the latter. This is 

 strikingly visible to the bark-peeler, or on the 

 accidental disbarking of a standing tree. In 

 both cases the cambium comes off with the bark, 

 leaving the surface of the wood completely de- 

 nuded, except small portions which remain in 

 the indentations and chinks of the latter. In the 

 case of a standing tree being disbarked, the 

 cambium gradually closes over the wound, in 

 the way previously described ; but if the naked 

 surface of the wood remains long exposed, and 

 becomes hardened by the air, though many new 

 layers of wood will be formed over it^ no intimate 

 union ever takes place between the layer that was 

 exposed and the new ; the scar ever remaining a 

 flaw in the timber : shewing that, notwithstand- 

 ing the cambium parts easily from the wood 

 when young, it forms a close union with it 

 while growing to perfection. The junction 



