54 



its proper pith or cellular ring outside it. 

 The green cellular or " herbaceous en- 

 velope" under the outer cuticle is sup- 

 posed to be the pith of the outer layer of 

 bark^ and to be to the layers of bark 

 what the central pith is to the layers of 

 wood ; and throughout its whole extent 

 there is probably a direct vascular com- 

 munication between this green external 

 pith of the bark and the internal central 

 pith of the wood;) by means of {he medul- 

 lary rays. This green parencJiymatous pith 

 of the bark is in communication with and is 

 in fact a continuation of the parenchymatous 

 parts of the leaves, (the spongy porous 

 partSj as distinguished from the woody 

 fibrous parts,) as the outer cuticle of the 

 stem is of the cuticle of the leaves and 

 buds. 



All physiologists talk of the circulation 

 of the sap ; and the expression must be 

 used, though it is a very incorrect one ; 

 that is, no one, I believe, has asserted, nor 



