Chap. III.] DOWNWARD GROWTH OF THE ROOT. 
125 
the bark and the internal central pith of the 
wood, by means of the medullary rays. This 
green parenchymatous pith of the bark is in com¬ 
munication with and is in fact a continuation 
of the parenchymatous parts of the leaves (the 
spongy porous parts, as distinguished from the 
woody fibrous parts), as the outer skin or 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 can we suppose any one to 
imagine, that there is a true circulation of the 
sap of plants, like that of the blood of animals. 
By the circulation of the sap is meant merely its 
ascent through the wood into the leaves and 
buds, thence into the green outer pith of the 
bark, on which the leaves and buds are situated, 
and its descent to the roots, through the living 
parts of the bark. How the descent dies off and 
stops, it is difficult to imagine; but it^is still 
more difficult to suppose that any part of the 
sap should re-ascend . The whole affair, how¬ 
ever, is a matter of the merest conjecture. 
The “ proper juices ” of plants are found in 
this green “ herbaceous envelope; ” for example, 
There is no true 
circulation of 
the sap like that 
of the blood of 
animals. 
