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of every particular year can seldom be accurately 
defined. 
The cortical layers are composed of fibrous parts 
which appear interwoven, and which are transverse 
and longitudinal* The transverse are membranous 
and porous, and the longitudinal are generally 
composed of tubes. 
The functions of the parenchymatous and cor- 
tical parts of the bark are of great importance. 
The tubes of the fibrous parts appear to be the 
organs that receive the sap ; the cells seem des^ 
tined for the elaboration of its parts, and for the 
exposure of them to the action of the atmosphere, 
and the new matter is annually produced in the 
spring, immediately on the inner surface of the 
cortical layer of the last year. 
It has been shown by the experiments of Mr* 
Knight, and those made by other physiologists, 
that the sap descending through the bark after 
being modified in the leaves, is the principal cause 
of the growth of the tree ; thus, if the bark is 
wounded, the principal formation of new bark is 
on the upper edge of the wound \ and when the 
wood has been removed, the formation of new 
wood takes place immediately beneath the bark : 
and every vessel and passage in the bark and wood 
of trees seems capable of carrying fluids in different 
and opposite directions, though more readily and 
copiously in one direction than in others, which 
offers something analogous to the anastomosis of 
vessels in animal bodies. A fact noticed by M. 
Palisot de Beauvois, is explained on this principle. 
That gentleman separated different portions of cor- 
