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T H E C O N S T R U C T I O N OF TIMBER
P L A T E
V I I I .
T h e common Pear Tree has afforded the in fiance from which the prefcnt views are
given. A piece of the wood of this tree, clean, pure, and perfedly feparated from
Fig. I. other fubftances, is ihewn at PLite VI I I. Fig. i. nothing can be fo f impl e ?,s its ftructure
: tho' difficult to obtain, there is little for obfervation in it when we have it:
only that truth is always valuable j and when we know the compoGtion of tlie wood
in one tree, we can undcrftand it in all.
T h e Wood then is fcarce any thing more than an arrangement of plain and fimple
tubes, refembling the tubes of the Blea; but that there are no mouths in themj nor is
there any of the interilitial floccofe matter between them more than what iills the very
fmall vacancies left by the roundnefs, between tube and tube : nay, even that difappears
as the wood grows harder j and finally, in feme trees, even the tubes themfelves;
their coats thickening both on the outfide and within, till neither cavity nor interflice
remains, but the whole is become one firm fubftance.
T h i s may be feen in a tranfverfe view of the common O a k ; fuch being chofen as
has grown on clay i for that from gravelly foils is much lefs compaft, lefs weighty,
and of very much lefs ilrength and value.
In the Pear, and in moft other Trees, fo much of the vafcular appearance remains
as always to make it eafy to underftand the ftruflure: we always fee vefTels, tho"
w i t h fmall apertures, arranged in lines the one behind the other, in many feries;
adhering firmly, and leaving fcarce any interftices.
When a piece of frefli Blea is torn from a Shoot, we have obferved that at the ragged
end, where the veffels have been broken off, they lofe their formj coilapfing, and no
longer appearing any thing more than flat threads : but 'tis not fo wi t h the more firm
and folid velTels which compofe the Wood : they feparate indeed in a piece torn thin,
but they keep their form and roundnefs, and break all together j not one by one;
nor forming a kind of pyramid, as in the Blea^ but an equal open termination. A
piece of the frelh Blea in this view is given a F i g . 2. t Plate V I I I . F i g . 2.
Fig- 3-
Fig. 4.
ii". ^
A t Fig. 3. is the reprefentation of a piece of the wood of the Bauhinia Aculeata,-
whofe difference appears very ftriking; but 'tis merely that of greater and lefs : the
veffels in this are extremely fmall, very hard, and laid unufually clofc together. The
whole viewed with the ufual powers of magnifying appears one compaS, uniform
mafs J but greater glaffes fliew it formed juf t as the others j only that there is fo little
o f the interflitial fubilance, that even in the youngefl: pieces the veffels feem to fill
the whole fpaces, by fuelling into them.
A t Fig. 4. is reprefented a Angle veffel of the wood of the Pear, clean feparated from
the other parts : this may be viewed all round, and thence we are confirmed the woodvefTelsare
mere clofe canals, with no lateral apertures. The plain and fimple hollow
is alfo very wel l feen in thefe fingle veffels. Art would in vain attempt to procure fuch :
they are too fmall to be the objedts either of the hands or eyes; but there never fail to
offer
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