NATURAL 
favourable to this supposition ; aud 
the existence of a power in the al- 
burnum, to carry the sap in different 
directions, is proved in the growth 
of inverted cuttings of different spe- 
cies of trees. But I have derived so 
“Many advantages, both asa gardener 
and farmer (particularly in the ma- 
nagement of fruit and forest trees) 
from the experiments which have 
been the subject of my former Me- 
moirs, that I am confident much 
public benefit might be derived from 
an intimate acquaintance with the 
use and office of the various organs 
of plants, and thence feel anxious to 
adduce facts, to prove that the con- 
clusions I have drawn are not in- 
consistent with the facts stated by 
my great predecessors. 
It has been acknowledged, I be- 
lieve, by every naturalist who has 
written on the subject (and the fact 
is, indeed, too obvious to be contro- 
verted) that the matter which enters 
into the composition of the radicles 
of germinating seeds, existed pre- 
viously in their cotyledons; and as 
the radicles increase only in length 
by parts successively added to their 
apices, or points, most distant from 
their cotyledons, it follows of neces- 
sity, that the first motion of the 
true sap, at this period, is down- 
wards; and as no alburnous tubes 
exist in the radicles of germinating 
seeds, during the earlier periods of 
their growth, the sap in its descent 
must either pass through the bark or 
the medulla. But the medulla does 
not apparently contain any vessels 
calculated to carry the descending 
sap, whilst the cortical versels are, 
during this period, much distended, 
and full of moisture; and as the 
medulla certainly does not carry any 
fluid in stems or branches of more 
than one year old, it can scarcely 
be suspected that it, at any period, 
HISTORY. 
935 
conveys the whole current of the de- 
scending sap. 
As the leaves grow, and enter on 
their office, cortical vessels, in every 
respect apparently similar to those 
which descended from the cotyle= 
dons, are found to descend from the 
bases of their leaves; and there ap- 
pears no reason, with 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 con- 
trary, rises wholly through the al- 
burnum and central vessels; for the 
destruction of a portion of the bark, 
in a circle round the tree, does not 
immediately, in the slightest degree, 
check the growth of its leaves and 
branches; but the elburnous ves- 
sels 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 in- 
verted 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, I selected, in several i 
stances, two poles of the same 
age, and springing from the same 
roots, in a coppice, which had been 
felled about six years preceding, and 
making two cireular incisions, at the 
distance of three 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 expe- 
303 Timent 
