T H E CONS T RUC T ION OF TIMBER
- C H A P . V.
O F THE BARK.
P L A T E HE Bark very much reiepibles the Rind in its confiruftion i nor can it indeed be
otherwife; for the Rind was once Bark, and has only fuffered a flight change in
feparating fropi it. Hapily the conftruaion of this eflentiai part is better feen in the
inner than in the outer coat of Trees i for it is more entire, more per fei t: and though, in
order of placc, tjie Rind could not but be firll deicribedj if may be averred, that unleis
this be firft viewed, the compofition of the other will be very difficultly diftinguiihed.
The Tree in which I have found the Bark moft happily formed for preparation, and
for obfervation, is the Vine. A piecc of this, feparated by maceration, and gbtained
Fig. I. pure and free from every other fubftance, appears as at Plate VI. Fig. i.
a ^ c Itconfifts plainly of veflels, ¿ j Blebs, ¿ j ^ d intermediate fpaces, f . The obvious
diiFerence between this and the outer Rind is, that the glebs are longer, and the velTels
appear more tender. This Bark, which we examine, is one time to be Rind : the Rind
that covers it is to fall off j this is to feparate from its inner coats, and be expofed to
the air in its place j and in this reparation the Blebs Ihrink in their length, and the
more immediate contad of the air gives a rigidity to the veflels.
Little need be faid farther of this j the former, 'which is the fame fubftance in another
condition, having been defcribed at large. It will be plain they are the fame when the
piece is applied to a greater microfcopic power: the mouths of the veffels are thus
ihewn yet more diitinitly in this than in the other ; becaufe they are here more perfe£
t i and the conilruition of the Blebs and their abfqlute feparate difpofition is better
feen, becaufe they ftand here farther afunder, the interftitial fpaces between Bleb
and Bleb having been made fmaller, as the Blebs were fliorter by the contradtion.
Kg. 2. Fig. 2.
Pig- 3- ^ Bleb, in its natural condition in the inner Rind, is ihewn at Fig. 3. It is a cylinder,
clofe at the bafe and o p ^ at the mouth, as is the univerfal conftruftion of all
Blebs of the Bark and Rind.
Fig. 4. At Fig. 4. is given" a tranfverfe fedion of the Bark, by v(hich its whole compofition
is feen to be nothing more than a number of coats, compofed each of one row of
Blebs, with velTels at their fides, laid very regularly over one another.