<iq 6 Mr. Knight on the inverted Action 
which I am acquainted, to suspect that both do not carry a 
similar fluid, and that the course of this fluid is, in the first 
instance, always towards the roots. 
The ascending sap, on the contrary, rises wholly through 
the alburnum and central vessels ; for the destruction of a 
portion of the bark, in a circle round the tree, does not im- 
mediately in the slightest degree check the growth of its 
leaves and branches : but the alburnous vessels appear, from 
the experiments I have related in a former Paper,* and from 
those I shall now proceed to relate, to be also capable of an 
inverted action, when that becomes necessary to preserve the 
existence of the plant. 
As soon as the leaves of the oak were nearly full grown 
in the last spring, 1 selected in several instances two poles of 
the same age, and springing from the same roots in a cop- 
pice, which had been felled about six years preceding ; and 
making two circular incisions at the distance of 3 inches from 
each other through the bark of one of the poles on each stool, 
I destroyed the bark between the incisions, and thus cut off 
the communication between the leaves and the lower parts of 
the stem and roots, through the bark. Much growth, as 
usual, took place above the space from which the bark had 
been taken off, and very little below it. 
Examining the state of the experiment in the succeeding 
winter, I found it had not succeeded according to my hopes ; 
for a portion of the alburnum, in almost every instance, was 
lifeless, and almost dry, to a considerable distance below the 
space from which the bark had been removed. In one in- 
stance the whole of it was, however, perfectly alive ; and in 
* Phil. Trans, for 1804. 
