338 Mr. Knight’s Experiments on 
riant shoot of the vine in my vinery, exactly in the stage of growth 
I wanted ; and this branch therefore was, towards its point, every 
day deprived of a small portion of its leaf. The bark, in conse- 
quence, became shrivelled and dry ; and at length the buds be- 
low vegetated ; and the point of the shoot died, apparently for 
want of nourishment. I here observed, as I had frequently done 
before, that almost the whole action of each leaf lies between 
itself and the root; for the branch, in this case, was perfectly 
well fed below the uppermost unmutilated leaf, but failed im- 
mediately above it. ’ P 
Every branch in which I had yet attempted to trace the pro- 
gress of the sap having contained its medulla uninjured, the 
action of that substance next engaged my attention, and I made 
the following experiments on the vine. Having made a passage 
about half an inch long, and a line wide, into a strong succulent 
shoot of this plant, I totally extracted its medulla, as far as the 
orifice I had made would permit me. But the shoot grew nearly 
as well as the others, whose medulla had remained uninjured ; 
and the wound soon healed. Making a similar passage, but of 
greater length, so that part extended above, and part below, a 
leaf and bud, I again extracted the medulla. The leaf and bud, 
with the lateral shoot annexed, (in the vine,) continued to live, 
and did not appear to suffer much inconvenience ; but faded a 
little when the sun shone strongly on them. 
I was now thoroughly satisfied, that the medulla was not 
necessary to the progression of the sap; but I wished to see 
whether the wood and leaf could execute their office when de- 
prived at once of the bark and medulla. With this view, I 
made two circular incisions through the bark, above and below 
a leaf; and I took off the whole of the bark between them. 
