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A Handbook of Biology

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Epidermis: It covers both the upper surface (adaxial epidermis) and

lower surface (abaxial epidermis) of the leaf. It has a conspicuous

cuticle. Abaxial epidermis generally bears more stomata than the

adaxial epidermis. The latter may even lack stomata.

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Mesophyll: The tissue between the upper and the lower epidermis. It is

made up of parenchyma. They contain chloroplasts for photosynthesis.

It has 2 types of cells:

Palisade parenchyma:

Adaxial epidermis

Palisade

mesophyll

Sub-stomatal cavity

Abaxial epidermis

Stomata

Phloem

Xylem

Bundle sheath

Spongy mesophyll

Air cavity

It is adaxially placed. Made up of elongated cells arranged vertically and

parallel to each other.

Spongy parenchyma:

The oval or round and loosely arranged. It is situated below the palisade

cells and extends to the lower epidermis. There are numerous large spaces

and air cavities between these cells.

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Vascular system: It includes vascular bundles. They can be seen in the

veins and midrib. Size of vascular bundles is dependent on the size of

the veins. The veins vary in thickness in the reticulate venation of dicot

leaves. Vascular bundles are surrounded by a layer of thick walled

bundle sheath cells.

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Xylem or protoxylem in dorsiventral leaves is directed or faces towards

upper epidermis.