Consists of three parts:

Epidermis, mesophyll and vascular bundles

Epidermis A single layered cells covering the leaf surface.

Consists of the upper epidermis and lower epidermis

LEAF

The main function of the epidermis is to protect tissues in the inner part of the leaf.

Cells in the upper epidermis do not contain chloroplasts except in the guard cells.

Cuticle is found on the surface of epidermal cells, including wax

In some plants, crystals (a form of waste material) are found in the epidermal cells.

Some plants possess stomata only in the lower epidermis, while in some plants stomata are found only in the upper epidermis e.g. aquatic plants

Generally, the lower epidermis is similar to the upper epidermis, except that the lower epidermis has more stomata.

Various forms of glands may be found in the epidermis.

Cross section of a leaf

trichomes

crystals

veins

Epidermal surface of a leaf

There are two guard cells around the stomatal pore. The guard cells are normally smaller than the surrounding epidermal cells and contain chloroplasts.

The function of stomata is to regulate the exchange of gas between the inner part of leaf and the atmosphere, as well as the evaporation of water that enters the plant through the roots.

Mesophyll The part which lies between the upper and lower epidermis.

Mesophyll cells contain numerous chloroplasts. Photosynthesis occurs mainly in the mesophyll tissue.

i) Palisade mesophyll which usually consists of two layers of elongated parenchyma cells that are closely packed in a vertical manner.

The mesophyll tissue usually are of two parts:

ii) Below is the spongy mesophyll that consists of irregular shaped parenchyma cells that are loosely packed, with abundant air spaces between them to allow more efficient air exchange.

Palisade parenchyma

perforations

A large lateral vein

Spongy mesophyll

Vascular bundles

Form the midrib and veins of various sizes in the

mesophyll. Consist of xylem and phloem tissues and

surrounded by thick walled parenchyma cells termed

the bundle sheath

The phloem transports carbohydrate manufactured by

mesophyll cells to all parts of the plant, while water

from the root is transported by the xylem to the leaf.

In monocot leaves, the mesophyll is often not

distinguished into the palisade and spongy layers.

In some monocots, e.g. in the Gramineae, there are

large cells with thin cell walls found on both sides of

the midrib, usually in the upper epidermis, called

bulliform cells.

Under dry condition, the bulliform cells shrink,

causing the leaf to roll, thus help reduce the rate of

transpiration from the leaf.

Bulliform cells (Gramineae)