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T H E CONSTRUCTION OF TIMBER
I I . T H E I R R E P E A T E D S E R I E S
I N THE P I SCIDI A C A R T H A G E N E N S I S.
P L A T E Tlie fineft view that it ispoffible to obtain of the Vafa intima of Trees, is that of
_ _ _! the Pifcidia Erythrina, given before, where the VelTels were examined as to their ftructnre,
in Plate XIII. but this other Pifcidia, the' much inferior to that, is not without
its fingularity or beauty. We have feen, in the Heliotrope, tliefe Veflels lodged in'
their proper place, the Blea : Nature has there allotted to the Shrub a fingle line of
i them : here we have two, ab-, and the fécond is in a place altogether Angular, the
Corona. The firll: and more natural feries of thefe Veflels is ranged in the centre of
the Blea : they are oval, large, and full of a juice, of a ilrong green, utterly unlike
and diftimft from all the other contents of the Branch. The repeated feries occupies
a confiderable fpace in the plain Corona of the Tree, where they have alfo loft their
oval form. They are perfeftly cylindric, as is'the moft natural form of thefe veffels;
and one would be led to doubt their nature, were it not afcertained by their contents;
the fame very green hard juice filling them.
What is farther obfervable in this fpecies, is, the extreme number both of the Vafa exà
à teriora, c, and of Sap-Veffels, d. There are feveral uneven ranges of the firft in the
fubftance of the Bark ; and the latter occupy, with the fame irregularity, a very great
f part of the Wood : yet is this Wood, e, pierced as it is like a cullender, not light, but
very heavy. We iliould wonder at this, had not thatfamiliar inftance, the Oak, taught
us that the flrength and weight of Timber is not affeâed by thefe apertures.
I I I . THE C E N T R A L D I S POS I T ION OF THE
I N THE HEMLOCK SPRUCE FIR.
P L A T E
X L I .
We have feen the Vafa exteriora enter the Pith, and ftain it with their contents, in the
Pious Cembra : and howfoever it be out of the common courfe to fee the Pith of Trees
pervaded by longitudinal Veflels, yet the Fir, known by the name of Hemlock Spruce,
will Ihew us that not the exteriora alone, but the intima, can find their way thither.
A feition of this Tree is given, Plate XLI. The exterior range of thefe VelTels is
formed, juil where it fhould be, in the Blea, a : they are fmall, but diftinguiihable enough
to an accudomed eye : they are perfeftly round ; their coats have a remarkable thicknefs
; and they are fluffed full of a firm, red refin, not a little refembling what druggifts
call dragon's blood. In the Pith we meet with Veffels, b, round in their out-line,
perfedlly diftinit in form from the cells of the Pith, and filled with this fame red refin.
It is impoffible not to recognize the Vafa intima in thefe: they ftain the whole of the
Pith, in cutting, with this juice : but the flight colour that acquires by accident, is very
eafily to be diftinguiihed from the deep and coarfe contents of the Veffels themfelves.
While this feftion is before us, it is impoffible but we muft ftop to admire the beautiful
conftrudion of the Wood, c, formed of lines drawn with a more than mechanical exaftnefs,
and enclofing little cones, d, pierced with innumerable Sap-Veflels, e. The Corona,
f , protuberates inward j and, in a thin ilice, is very diftindh
C H A P .