Page 102 - Pharmacognosy 2 PG303 (1)

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

9- Pith: it may be solid or have central hollow e.g. Belladonna and Henbane.

II- Microscopical Characters

1- Young herbaceous stem of dicotyledons or of gymnosperms:
It is composed of outer most layer termed the epidermis, followed by the cortex which
limited in the inner side by a layer of peculiar structure called endodermis. Within the cortex a
central cylinder or stele which consists of open vascular bundles i.e. with cambium arranged in a
single ring around central region called pith or medulla and separated from the endodermis by a
tissues called the pericycle. Running between the vascular bundles from pith to cortex are a number
of parenchymatous strands called primary medullary rays. The ground tissues of the stem is
composed of the cortex, pith and medullary rays. The vascular bundles maybe frequently
connected through the medullary rays by the interfascicular cambium and sometimes through the
activity of this cambium, they are forming a continuous ring with the primary xylem directed
towards the pith.

2- Monocotyledonous stem:
It differs from dicotyledons stem in that it shows many closed vascular bundles scattered
irregularly through the ground tissues. They are usually smaller and more crowded together near
the periphery of the stem than in the center, where they are commonly larger and less in number.
The pith, medullary rays, the limit of cortex, and pericycle are often indistinguishable.

1- Epidermis: usually comosed of a single row of cells that vary in size and shape. They exhibit
tangential elongation in transverse sections and axial elongation in longitudinal sections. It
generally bears stomata and hairs (glandular and non- glandular) and covered with cuticle.
2- Cortex: It is narrow in Dicots and almost absent in monocots, and generally composed of
parenchymatous cells which in transverse section, are tangentially elongated near the
epidermis but more isodiametric near the endodermis and generally exhibited intercellular
spaces. It may be differentiated into the following layers:
Hypodermis: is usually collenchymatous in nature and devoid of contents.
Ground parenchyma: outer region usually contain chloroplasts (chlorenchyma), while
middle region may show sclerenchyma, secretory structures (oil cells, glands or laticeferous
ducts) or idioblasts of calcium oxalate crystals, tannin, ……. etc.
Endodermis (the innermost layer of cortex): the cells are similar to those of the epidermis
in shape, but their walls are suberized and may show cutinized or lignified casparian strips
e.g. Lobelia and may contain starch granules (starch sheath) e.g. Solanaceous herbs.

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