Chap. II.] 
C0U11SE OF THE SAP. 
85 
rupted at each node or annual shoot by a kind 
of woody partition,” if this fact of De Candolle’s 
is true, what becomes of his theory , that the pith 
is the cotyledon of the bud. 
I do not think it would be an improper de¬ 
scription of the piths of these trees to say that 
their spongy piths begin with, or are seated on, 
cheesey pith, and end in cheesey pith, on which 
the bud is seated. 
The only opinion which I should venture to 
express, in reference to the pith, is the negative 
one, that no one has as yet discovered its offices. 
If this is so, it is not saying much for our know¬ 
ledge of vegetable physiology. 
Were the upward sap supplied to each branch 
by longitudinal channels from the root, peculiar 
to that branch, the pruning or cutting out of 
branches would not benefit the leader and the 
remaining branches. The growth of these is, 
however, increased by judicious and gradual 
pruning, because the channels for the upward 
sap from the root are not peculiar, but general, 
through the whole wood of the stem, to every or 
any part or side of it, where nature, or chance, 
or art , allows it an outlet for growth and elabo¬ 
ration. 
The reason of the extraordinary strength of 
Office of the 
pith not known. 
As the sap- 
channels are 
general, not 
peculiar, prun¬ 
ing increases 
the supply to 
the leader, &c. 
