90 



LETTERS ON TREES. 



we regard and speak of as timber; and while for many 

 purposes immense aggregations of this kind are needed, 

 they could have been produced only, consistently with 

 a strict adherence to the general analogy of vegetable 

 life, by such pecuharities in the modes and habitudes 

 of growth of the various tree-plants as it has been my 

 object in these Letters to point out as belonging to 

 them. 



21. In truth, then, as I believe, just as we have 

 annually a crop of corn, so have we annually a crop of 

 timber; and just as we stack the one or put it into 

 barns of our own building, so does nature stack the 

 other for us, laying it up and preserving it in a 

 way we cannot, leaving it to ourselves to draw from 

 her store, and turn it to our purposes as we need, or 

 as we please, after the stack has stood ten, or fifty, or 

 a hundred, or a thousand years. A tree is but a 

 timber-stack of nature's building. 



22. .But however this may be, the fact is, as we have 

 seen, that after its formation the woody matter of a 

 tree undergoes no such molecular change of substance 

 as we have reason to believe essential to the continu- 

 ance of vitality in any organised structure. And to 

 this it may be added, that after the year of their 

 formation, the several layers of wood and root undergo 

 no farther extension by growth. So .unchanged do 

 they remain, that from an examination of the woody 

 cylinders of an old tree, we may readily gather, nay 



