of the alburnous Vessels of Trees. 127 
sive of the immediate action of the latter substatice; and the 
whole of this will stagnate on the lower lip of the wound, 
where I conceive it generates the small portion of wood and 
bark, which Hales and Du Hamel have described. 
I should scarcely have thought an account of the preceding 
experiments worth sending to you, but that many of the 
conclusions I have drawn in former memoirs appear, at first 
view, almost incompatible with the facts stated by Hales and 
Du Hamel, and that I had one fact to communicate relative 
to the effects produced by the stagnation of the descending 
sap of resinous trees, which appeared to lead to important 
consequences. I have in my possession a piece of a fir tree 
from which a portion of bark, extending round its whole 
stem, had been taken off several years before the tree was 
felled; and of this portion of wood one part grew above, 
and the other below, the decorticated space. Conceiving 
that, according to the theory I am endeavouring to support, 
the wood above the decorticated space ought to be much 
heavier than that below it, owing to the stagnation of the 
descending sap, I ascertained the specific gravity of both 
kinds, taking a wedge of each as nearly of the same form as 
I could obtain, and [ found the difference greatly more than 
Thad anticipated, the specific gravity of the wood above the 
decorticated space being 0°590, and of that below only 0-491; 
and having steeped pieces of each, which weighed a hundred 
grains, during twelve hours in water, I aie the latter hae 
absorbed 69 grains, and the former only 51. 
The increased solidity of the wood above the decorticated 
Space, in this instance, must, I conceive, have arisen from 
' the stagnation of the true sap in its descent from the leaves ; 
and therefore in felling firs, or other resinous trees, consi- 
derable advantages may be expected frem stripping off a por- 
tion of their bark all round their trunks, close to the surface 
of the ground, about the end of May or beginning of June, 
_in the summer preceding the autumn in which they are to 
be felled. For much of the resinous matter contained in 
the roots of these is probably carried up by the ascending 
sap in the spring, and the return of a large portion of this 
matter 
/ 
