rind of the birch into fix dlftihft coats, and that he had no dcsibt
but what the divifion might have been carried much further.
Dr. Hill fays, that unlefs forne 'of thefe coats are obtained in a
jftate of feparation from the reft, the true conftruction of the rind
cannot be difcovered, for the connection and form of the parts is
loft by the confufion in which they appear while they lie one
upon another.
The following experiments may throw a little light upon this
obfcure fubjeft.* All the rind was taken from the trunk of a
cherry tree, and the tree thus Ikinned, expofed to the air, a part
o f the bark which was next to the rind dried up and exfoliated ;
the part next to this did the fame ; after two or three exfoliations,
a farinaceous fubftance covered the fuperficies of the trunk, foon
after which a new rind appeared. Some pieces, o f rind were
taken from a few young branches, and the wounds were covered
with a cloth that had been foaked in wax and turpentine; on thefe
the rind appeared in a very little time, without any apparent exfoliation.
From fome other branches, not only the rind, but a
part of the bark, was allb taken away, and the wounds covered as
before; a flight exfoliation was obferved here, which was foon
followed with a new rind. The bark was taken entirely off from
a vigorous cherry-tree, while it was in full fap, fo that the wood
appeared the whole extent o f the trunk. This was protected
from the rays o f the fun, and from the air. A new bark and
rind formed themfelves upon the trunk, but they did not originate
from the bark that was left on the branches and the root, but
extended from different fpots, which were firft formed at confiderable
Duhamel Phyfique des ArbreS, tom. .1, p. 12.
fiderable diftances from each other. After a lapfe of fifteen
years, this new rind did not appear like the natural rind of the
cherry-tree. From thefe experiments we learn, that the rind regenerates
more readily in fome cafes than in others, and that it
preferves and prevents in a degree the bark from becoming dry
too foon, and in confequence thereof exfoliating.
Aided by the microfcope, a number o f luminous points may
be difcovered in the rind;* thefe are fo many minute.holes for
other purpofes o f tranfpiration. In the cane thefe holes are vifible
to the naked eye. A few oval holes may alfo be perceived in i t ;
thefe are, however, no more than a feparation of the parts, oc-
cafioned by the extenfion of the vafa interiora.
Dr. Grew fuppofed the rind to be formed of fmall veficles, or
bladders, cluttered together, and intermixed with lignous fibres
or veffels, which run through the length of the rind; thefe are
conjoined by other tranfverfe ones, but that as the rind dries, the
bladders or blebs Ihrink up and difappear. This account does
not differ much from that of Dr. Hill, who fays, that the rind is
formed of a feries of longitudinal veffels, and a filmy fubftance
between them, which, when viewed in a tranfverfe feftion, form
fmall circles, the fides o f which are fupported and made up o f
thefe longitudinal fibres; that the tranfverfe veffels are only a deception,
occafioned by the fpaces between part and part o f the
film. The mode of obtaining an accurate view o f the organization
of this part, by conveying coloured liquors into the feveral
veflels thereof, has been already defcribed in page 162 o f thefe
4 L eflays;
* Duhamel Phyfique des Arbres, vol. i, p. 9«