Page 6 - Pharmacognosy-I (02-06-06-102)

Microscopical Structure of the Leaf:

Internal structure of leaves reveals the three tissue systems namely,
the epidermal, cortical and vascular systems:

1-The epidermis:
• a protective layer: it may contain stomata or trichomes.
• Leaves contain a lower epidermis and an upper epidermis.
• Trichomes or hairs, they are either covering (non-glandular)

or glandular trichomes.

Non-Glandular (covering) Trichomes:
They may be Unicellular or Multi-cellular.

Stomata:
- The leaf epidermis is covered with pores called stomata.
- Function: regulates the exchange of gases and water vapor

between the outside air and the interior of the leaf.
- Typically, the stomata are more numerous over lower epidermis

than upper ones.
- They offer important diagnostic characters for the identification

of many leaf drugs.

According to the characters and arrangement of the surrounding

epidermal cells, stomata are classified into:

A. Anomocytic B. Paracytic

C. Diacytic D. Anisocytic

2-The cortical tissue:
It is the whole parenchymatous tissue between the two epidermal
layers.
Mesophyll:
It is undifferentiated in case of monocot leaf
It is usually differentiated in dicot leaf into:

• Palisade: cylindrical, columnar cells, perpendicular to the
epidermis and contain chloroplasts.

• Spongy tissue: closely packed chlorenchyma.

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