Page 158 - Pharmacognosy 2 PG303

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

brown scale leaves arising at the nodes, and having usually a large apical bud
and small axillary ones. The daughter corm is protected below the large apical
bud, being situated above the parent corm as in Crocus and Colocasia, or below
one of the side buds as in Colchicum.

3. Stem tuber: It is a swollen underground stem or part of stem usually its
tip. It differs from root tuber in bearing several small scales and buds forming
sometimes what is called eyes, as well as terminal bud on the free end as in
potato. It is full of food material and serves in vegetative propagation.

4. Bulb: It is an underground stem which is reduced to a small, flattened disc
and is crowned with crowded fleshy scale leaves or scale leaf-bases and having
adventitions roots arising from the base of the bulb. The bulb may be a scaly bulb
(imbricate bulb) or a tunicated blub. In the scaly bulb, the fleshy scales, of which
the main bulk of the bulb is composed, nearly overlap with their margins (the outer
scales are not encircling the inner ones) as in Iilium. In the tunicated bulb, the outer
scales are large and completely en-sheathing the inner portion of the bulb. The
outer covering or the tunic is formed of the brownish membranous scales: formed
by the shriveled remains of the leaves of the previous season.

Histology of Subterranean Stems
They generally resemble in structure the aerial stems, although they are

115