262 PHYSIOLOGY OF TREES. 



bered, that a lofty tree, wiien it first receives the 

 enlivening impulse of spring, has its bark closely 

 embracing the surface of the alburnum. The 

 first signs of life are the bursting buds exter- 

 nally, and the liquefaction of the sap internally. 

 Soon after this, the bark is raised from the wood 

 by the expansive power of the sap, now assuming 

 the appearance and receiving the name of cam- 

 bium, and shewing itself at the bottom of the 

 lofty trunk almost as soon as it does at the top : 

 we cannot conceive, therefore, how the descend- 

 ing radicles can reach so far down in so short a 

 time : — how they should descend the distance of 

 sixty or eighty feet in a few days is incon- 

 ceivable. Another question follows : how does it 

 happen that the new layer of liber is formed out 

 of these descending radicles so distinctly and 

 separately from the body of the new alburnum, 

 as well as from the last year's liber? And 

 whence some of the gems which so soon after 

 appear to rise from these descending radicles? 

 Such phenomena may take place ; but the expla- 

 nation is difficult. 



