80 



LETTERS ON TREES. 



farther, that they are essentially independent, that is, 

 physiologically, or in respect of their vital relations, of 

 the stock on which they grow. 



2. That at the close of the year the young plants 

 die, and never afterwards live, is sufficiently obvious 

 as regards the leaves and flowers, which wither, fall 

 off, and completely disappear. How large a part these 

 form of the whole annual vegetation of a tree, it is 

 unnecessary to insist upon. The only question, there- 

 fore, is as to what remains of the other parts of the 

 plants — viz. the roots and stems. 



3. Now on what grounds are we entitled to affirm 

 that these stems and roots then die and never live 

 again ? 



4. To pave the way for the evidence to be adduced, 

 let us dwell for a little on some considerations con- 

 nected with general physiology, comparing and con- 

 trasting, as we proceed, animals with vegetables, and 

 the everlasting trees producing timber for the use of 

 man, with the annual corn-plants which supply him 

 with his daily bread. 



5. Consider, then, first of all, what is true of the 

 whole organised creation, of vegetables equally with 

 animals, of animals in common with vegetables, that 

 all vital action is of exceedingly short duration in any 

 organised structure. The chemical affinities by which 

 the various organic compounds are formed, and the 

 plastic affinities by which these compounds are subse- 



