ITS COMPOSITE NATURE. 137 



munication, by means of the newer layers of wood, with the fresh 

 rootlets, which are alone active in absorbing the crude food of the 

 plant from the soil. The fluid they absorb is thus conveyed direct- 

 ly to the branches of the season, which alone develope leaves to 

 digest it. And the food they receive, having been elaborated and 

 converted into organic nourishing matter, is partly expended in the 

 upward growth of new branches, and partly in the downward for- 

 mation of a new layer of wood, reaching from the highest leaves 

 to the remotest rootlets. These two essential organs, namely, the 

 rootlets which absorb, and the leaves which digest, the plant's 

 nourishment, are, therefore, annually renewed ; and, whatever 

 their distance or the age of the tree, are maintained in fresh com- 

 munication through the new annual layers. As the exogenous 

 tree, therefore, annually renews its buds and leaves, its wood, 

 bark, and roots, every thing, indeed, that is concerned in its life 

 and growth, there seems to be no reason, no necessary cause in- 

 herent in the tree itself, why it should not live indefinitely. Ac- 

 cordingly, several trees are known to have lived for a thousand 

 years or more ; and others are now living which are with high 

 probability thought to be above two thousand years old.* This 

 longevity, however, will not appear surprising when we remember 

 that 



229. The Plant is a Composite Being, or community, lasting, in 

 the case of a tree especially, through an indefinite and often im- 

 mense number of generations. These are successively produced, 

 enjoy their term of existence, and perish in their turn. Life passes 

 onward continually from the older to the newer parts, and death 

 follows, with equal step, at a narrow interval ; no portion of the 

 tree is now living that was alive a few years ago ; the leaves die 

 annually and are cast off, while the internodes or joints of stem that 

 bore them, as to their wood at least, are buried deep in the trunk, 

 under the wood of succeeding generations ; converted into heart- 

 wood they are equally lifeless, or perchance decayed, while the 

 bark that belonged to them is in time thrown off from the surface. 



* The subject of the longevity of trees has been ably discussed by De Can- 

 dolle, in the Biblioth&gue Universelle of Geneva, for May, 1831, and in the 

 second volume of his Physiologic Vigitale: also, more recently, by Prof. Al- 

 phonse De Candolle. In this country, an article on the subject has appeared 

 in the North American Review, for July, 1844. 

 12* 



