317 
the Alburnum of Trees , 
proved that such infusions do not penetrate the cellular sub- 
stance of the alburnum, the evidence which this circumstance 
would afford would be very defective. 
Amongst other experiments that I made to ascertain whe- 
ther the cellular substance of the alburnum would imbibe 
coloured infusions, I took off branches of two years old with 
the annual shoots and leaves attached to them, in the summer, 
from trees of different species ; and I effectually closed the 
alburnous tubes with a composition formed of calcined oyster 
shells and cheese,* and this was covered with a mixture of 
bees wax and turpentine, so as to effectually exclude all mois- 
ture. A part of the bark was taken off each branch, in a 
circle round it, a few lines distant from its lower end, where 
the tubes had been closed ; and each branch was then placed 
in a decoction of logwood, in a vessel deep enough to cover 
the decorticated spaces. At the end of twenty hours, or some- 
what longer periods, these branches were examined, and the 
coloured infusion was found to have insinuated itself between 
the alburnous tubes, in many instances apparently through 
the cellular substance. This was most obvious in the walnut 
tree, the young wood of which is very white. The principal 
object I had in view in making this experiment, was to detect 
the passages through which I conceived the sap to pass from 
the bark into the alburnum.f 
From the preceding circumstances, I am disposed to infer 
that the sap secretes through the cellular substance of the 
alburnum ; and through this I conceive that it must ascend 
* I have found this composition, and this only, to be capable of instantaneously- 
stopping the effusion of sap from the vine, or other tree, in the bleeding season. 
\ Phil. Trans. 1807, p. 7. 
