LETTER XI. 



115 



obstruction of the channels which permeate it, did not impede 

 the circulation of the sap^ and consequently its access to the 

 liber. 



" In fine, what we call death by old age in a tree, to speak 

 correctly, is the extinction of that portion of a race which has 

 been carried on by continuous evolution ; the inevitable result 

 of an incidental death in the liber, occasioned by the privation 

 of nourishment. 



In proportion as a tree increases in size, the vessels of its 

 ligneous layers become obstructed, and the sap circulates with 

 less freedom. Hence absorption and secretion . decrease after 

 youth, in proportion as the bulk of the tree is enlarged. The 

 liber is less vigorous ; the buds and roots become fewer and 

 feebler ; the branches wither ; the stem decays at the head ; 

 water settles in the injured parts ; the wood moulders away. 

 Ere long, the new liber, the annual herbaceous part of woody 

 vegetables, loses the power of completing its regeneration, 

 new parts are no longer evolved, and the tree perishes." 



13. But thougli the tree finally perishes, it is not 

 from old age. It is from purely accidental causes. 

 M. Mirbel has already told us that the tree is in its 

 own nature as imperishable as a race^ or as that por- 

 tion of a race which constitutes do family, or a house, a 

 lineage or a clan. But it is needless to dwell on the 

 details comprised in M. Mirbel's paper. I have under- 

 lined those expressions in it which bear more directly 

 on the views unfolded in these letters. Further com- 

 ment than this seems to me superfluous. You can 

 yourselves make the application of them to my views. 



I shall only observe that, while, in M. Mirbel's mind, 



