Page 159 - Pharmacognosy 2 PG303

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

either devoid of or contain only very little sclerenchymatous tissue. In
Dicotyledons, however, the rhizomes and other underground stems show large
pith and wide cortex, formed mostly of thin-walled parenchyma packed with
reserve materials. The cortex is traversed by very few vascular bundles of the leaf-
and root-traces and the endodermis is usually indistinguishable with a few
exceptions as in valerian. The vascular bundles, which are open, generally remain
widely separated by wide medullary rays, and form a single ring around the pith.
In some cases, as in the subterranean stem of Liquorice and lpecacuanha, the
secondary vascular elements are produced in great amount forming a continuous
radiate ring around the pith.

In Monocotyledons, the structure differs from that of the aerial stem. It shows
a distinct endodermis separating a clear cortex from the central stele. The vascular
bundles are closed and usually numerous, being scattered in both the cortex and the
stele but generally more crowded and smaller within the endodermis and larger and
few in the centre. Sometimes the rhizome is hollow and the vascular bundles are
mainly restricted to the layer within the endodermis where they are embedded in
sclerenhyma, it also shows sclerenchymatous hypodermis as in Couch grass.

Subterranean stem. I,corm of Colchicum:a,axis.of the flowering
shoot;b,bud for next season stem; e, brown envelop scales; f, remains
of flowering stem of last season; o, ovary; s, scar of parent corm; v,
vascular bundle; II -scaly bulb of Lilium; III, vertical section of same;
IV, corm of Colocasia (ad. r, adventitious root; s. l, scale leaf; n. c, next

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