Inconvertibility of Bark into Alburnum. 105 
alburnum, beneath the transposed bark, appeared perfectly 
similar to that of other parts of the stock, and the direction 
of the fibres and vessels did not in any degree correspond 
with those of the transposed bark.* 
Repeating this experiment, I scraped off the external sur- 
face of the alburnum in several spaces, about three lines in 
diameter, and in these spaces no union took place between 
the transposed bark and the alburnum of the stock, nor was 
there any alburnum deposited in the abraded spaces ; but the 
newly generated cortical and alburnous layers took a circular, 
and rather elliptical, course round those spaces, and appeared 
to have been generated by a descending fluid, which had 
divided into two currents when it came into contact with the 
spaces from which the surface had been scraped off, and to 
have united again immediately beneath them. 
In each of these experiments, a new cortical and alburnous 
layer was evidently generated ; and apparently by the same 
means that similar substances were generated beneath a plaister 
composed of bees-wax and turpentine, in former experi- 
ments ;-f and the only obvious difference in the result appears 
to be, that the transposed and newly generated bark formed 
a vital union with each other : and it is sufficiently evident, 
that if bark of any kind was converted into alburnum, it must 
have been that newly generated. For it can scarcely be sup- 
* Duhamel having taken off, and immediately replaced, similar pieces of the 
bark of young elms, subsequently found that the alburnum, which was generated 
beneath such pieces of bark, had not formed any union with the alburnum of the tree, 
beneath it. But this great naturalist did not employ ligatures of sufficient power to 
bring the bark and alburnum into close contact, or the result would have been dif- 
ferent. 
f Phil. Trans, for 1807. 
MDCCCVIII. P 
