Page 237 - Pharmacognosy 2 PG303 (1)

Pharmacognosy-2 (PG303) Level 2 Clinical Pharmacy-Pharm D

a grayish white matrix. The smoothed transverse surface usually shows near the
periphery an occasional dark cambium line, followed by a radiating narrow
xylem, numerous star spots scattered, or in a more or less diffuse ring. Each star
spot is composed of a central phloem and dark red lines, radiating from a
common centre through a grayish-white ground tissue. Pith is large, grayish white,
with scattered irregular star spots and reddish-brown lines.

Microscopical Characters
Cortex, if present, is very narrow, consisting of polygonal cells containing
simple or compound starch granules and idioblasts with large cluster crystals of
calcium oxalate. Phloem, if present, is parenchymatous, traversed by reddish
brown medullary rays, 2-5 cells wide, with reddish brown contents and showing
numerous idioblasts with large cluster crystals of calcium oxalate. Phloem
parenchyma contains starch granules. Sieve tubes, represented in scattered
groups, mostly obliterated. Xylem, forms a narrow ring within the cambium, and
is traversed by parenchymatous medullary rays, usually 2-3 cells wide, with
brownish amorphous contents which are insoluble in alcohol (90%), soluble
in water and in chloral hydrate T.S. The vessels are non-lignified, isolated or
in groups, up to 160 mostly 80 µ in diameter, with reticulate, spiral or annular
thickening. Pith consists mostly of parenchyma and irregularly traversed by star
shaped, amphivasal, abnormal vascular bundles (star spots), consisting of dark
reddish brown medullary rays radiating through a central grayish-white
phloem with collapsed sieve tubes and continue through the peripheral xylem.
The latter consists of slightly wide non-lignified reticulate thickened vessels.
Mucilaginous cavities may be found in the phloem of the star spots. The root
shows the same ground tissue calcium oxalate crystals and starch granules as
the rhizome.

T. Cut. in Rhubarb; a, periderm; b, phloem; c, cambium;
d, xylem; e, star spot; f, pith.

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