Inconvertibility of Bark into Alburnum. 109 
necessarily have been covered by every successive layer of 
alburnum, without any transmutation of bark into that sub- 
stance.* 
In the second experiment cited by Mirbel, Duhamel has 
shewn that when a bud of the peach tree, with a piece of bark 
attached to it, is inserted in a plum stock, a layer of wood 
perfectly similar to that of the peach tree will be found, in 
the succeeding winter, beneath the inserted bark. The state- 
ment of Duhamel is perfectly correct; but the experiment 
does not by any means prove the conversion of bark into 
wood ; for if it be difficult to conceive ( as he remarks ) that 
an inserted piece of bark can deposit a layer of alburnum, it 
is at least as difficult to conceive how the same piece of bark 
can be converted into a layer of alburnum of more than twice 
its own thickness (and the thickness of the alburnum deposited 
frequently exceeds that of the bark in this proportion), with- 
out any perceptible diminution of its own proper substance. 
The probable operation of the inserted bud, which is a well 
organized plant, at the period when it becomes capable of 
being transposed with success, appears also, in this case, to 
have been overlooked, for I found that when I destroyed the 
buds in the succeeding winter, and left the bark which be- 
longed to them uninjured, this bark no longer possessed any 
power to generate alburnum. It nevertheless continued to 
live, though perfectly inactive, till it became covered by the 
successive alburnous layers of the stock ; and it was found 
many years afterwards inclosed in the wood. It was, how- 
ever, still bark, though dry and lifeless, and did not appear 
to have made any progress towards conversion into wood. 
* Physique des Arbres, Lib. IV. Ch. III. 
