Page 244 - Pharmacognosy 2 PG303

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

1. Liquorice root; a, unpeeled; b, peeled.
2. Stolon T. cut; a, cork; cortex; c, cambium; d, xylem; e, pith

Microscopical Characters
Cork is thick, brown or purplish brown, and formed of several layers of
flattened polygonal, thin-walled cells. The cortex, of phelloderm in root, is
somewhat narrow, yellow of parenchyma cells, containing isolated prisms of
calcium oxalate. Phloem is wide yellow, traversed by numerous, wavy
parenchymatous medullary rays, 1-8 cells wide, and consisting of numerous radial
groups of fibers. Each is surrounded by a sheath of parenchyma cells, each usually
containing a prism of calcium oxalate, and alternating with layers of parenchyma
and sieve tissue. The latter is occasionally obliterated, appearing as refractive
irregular structure. Phloem fibers are very long, with very narrow lumen and
strongly thickened, stratified walls, which are cellulosic in the inner part of the
phloem and slightly lignified in the outer. Xylem is yellow, distinctly radiate. The
rays of xylem consist of a little pale-yellow parenchyma, groups of fibers
similar to those of the phloem, but more lignified and surrounded by crystal
sheaths, tracheids and large wide lumen vessels, 80-200 µ in diameter, with thick,
yellow reticulate walls or with numerous oval bordered pits with slit-shaped
openings. Other parenchyma cells contain small round or oval starch granules. Pith,
only in rhizome, is dark yellow parenchymatous. Root shows 4-arch primary xylem,
with no pith and shows 4 broad primary medullary rays, radiating from the center,
at right angles to one another. In the peeled liquorice, the cork, cortex, and
sometimes part of the phloem is absent.

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