ON THE DESCENT OF THE SAP. 
381 
After carefully reading your remarks upon the motion of the sap, 
and your objections to the different theories, I do not perceive that you 
have advanced any one of your own. You confess that all your 
experiments have led to negative rather than affirmative conclusions. 
This is certainly very candid. You say, however, that you do not 
deny occasional or partial sinkings of the sap. Upon what principle 
do you then account for these partial sinkings ? I really do consider 
it more philosophical, and more in consonance with the phenomena of 
organised existence, to admit at once a principle of regularity of move¬ 
ment, than to consider that these wonderful developments are effected 
by any process bordering upon being fortuitous. You seem to abjure 
the opinion of the regular descent of the elaborated sap, merely because 
you cannot account for it upon the general laws of fluids and mechanics. 
I make little doubt but we shall find, as we become better acquainted 
with vegetable anatomy, that the flow of the sap takes place in unison 
with the principles of fluids and mechanics ; but shall we on this 
account come to the conclusion that these laws have any other connexion 
with organised existence than that of being wholly subservient to its 
purposes? Admit that vegetables are endowed with a vital principle, 
and you must allow you are then treating of something vastly superior 
to a mere machine or the most perfect chemical apparatus. The 
circumstances connected with ligatures and ringing, to which you 
frequently refer, go far to confirm a descending as well as an ascending 
fluid, and that both are in constant operation. If, as some allege, 
every part of a plant has the power of elaborating and appropriating to 
itself the necessary supply of sap as it rises from the roots—an opinion 
in which you seem partly to concur-—how comes it that, in the case of 
ringing, the plant almost invariably attempts to heal up the deficiency 
by making advances from the upper side, while little or no advances 
are made from the under side—if it proceed not from an accumulation 
of sap that has been stopped in its downward course ? Here it may 
be asked, how, upon this principle, there should be any advances at all 
made from the under side. There is certainly a difficulty in accounting 
for this at first sight, but it is greatly removed when we think of the 
abundant proofs we possess, that there is in the vegetable as well as in 
the animal economy not merely an accommodating principle, enabling 
plants to suit themselves to circumstances, but a powerful energy ever 
ready to be put in requisition for the healing of a wound, making good 
a loss, or maintaining an existence. A host of interesting confirmatory 
facts might easily be adduced. Besides, we are agreed that, besides 
the leading channels through which the sap flows, it also is diffused 
in every direction through the vascular and cellular texture, and, 
