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 



