Page 261 - Pharmacognosy 2 PG303 (1)

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

cells, with occasional sclereids. Phloem is wide, largely developed, formed mainly
of parenchyma, containing starch granules and showing small scattered groups of
sieve tissue, but no fibers. Primary phloem consists of 5-8 bundles, within the
pericycle and alternating with the angles of the cambium. Xylem is only slightly
developed, represented by a group of primary xylem, with wedged-shaped groups,
of secondary xylem, forming a. nearly V-shape, within each angle of the stellate
cambium and enclosing between the arms parenchymatous medullary ray cells. Also
small groups of secondary xylem occur along the cambium line, especially in the
thick parts of the tuber. Primary xylem shows spiral vessels and secondary xylem,
with reticulate and pitted vessels. Pith is formed of large, rounded parenchyma cells,
filled with starch granules. Medullary rays are indistinctly differentiated. Stem bases
show epidemis with thin anticlinal and thick outer walls, parenchymatous cortex,
pericycle with continuous ring of groups of thick-walled fibers, connected with
groups of sclerenchymatous cells and showing few gaps. Vascular bundles are
collateral, about 30-60 in a ring, each capped with a group of pericyclic fibers; pith,
of aerenchyma, surrounding a large central lacuna

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