322 
PHYSIOLOGY. 
BOOK II. 
Another case was, that if a large ring of bark be taken 
from the trunk of a vigorous elm or other tree, without being 
replaced with any thing, new beds of wood will be found 
in the lower as well as upper part of the trunk ; while no 
ligneous production will appear on the ring of wood left ex- 
posed by the removal of the bark. Now this is so directly at 
variance with the observations of others, that it is impossible 
to receive it as an objection until its truth shall have been 
demonstrated. It is well known, that, if the least continuous 
portion of liber be left upon the surface of a wound of this 
kind, that portion is alone sufficient to establish the commu- 
nication between the upper and lower lips of the wound ; but, 
without some such slight channel of union, it is contrary to 
experience that the part of a trunk below an annular incision 
should increase by the addition of ne^ layers of wood until 
the lips of the wound are united, unless buds exist upon the 
trunk below the ring. The horizontal parenchymatous system 
may, however, go on growing, and so form new layers. 
Dutrochet mentions some cases of extraordinary longevity 
in the stock of Pinus Picea, after the trunk had been felled, 
and which he supposes fatal to the theory of wood being 
formed by the descent of organised matter. He says that, in 
the year 1836, a stock of Pinus Picea, felled in 1821, was 
still alive, and had formed 14 thin new layers of wood, that 
is, one layer each year; and another, felled in 1743, was still 
in full vegetation, having formed 92 thin layers of wood, or 
one each year. But, in reality, these cases prove nothing more 
than that the stock of Pinus Picea is singularly tenacious of 
life ; for, although M. Dutrochet does not say so, there can 
be little doubt that these layers of wood were a parenchy- 
matous developement of the horizontal system. (See Comptes 
rendus^ iii. 748.) 
Those who object to the theory of wood being generated by 
the action of leaves either suppose, — 1 st, that liber is deve- 
loped by alburnum, and wood by liber ; or, 2dly, that “ the 
woody and cortical layers originate laterally in the cambium 
furnished by pre-existing layers, and nourished by the de- 
scending sap. The first of these opinions appears to be that 
of Turpin, as far as can be collected from a long memoir upon 
