Decribe the internal structure of a dorsiventral leaf with the help of labelled diagrams.

Explanation

The section of a dorsiventral leaf (sunflower leaf) is stained through safranin and viewed under microscope then following structure is seen:
(1) Epidermis, (2) Mesophyll tissue, (3) Vascular bundles.
(1) Epidermis : A leaf being a flat organ, there are two epidermis seen in it:
(i) Adaxial epidermis, (ii) Abaxial epidermis.
(i) Adaxial Epidermis: It is a single layer made up of parenchymatous cells. This protective skin is located on outer wall of cells of this layer. It does possess stomata. Respiratory cavity is present inside of stomata.
(ii) Abaxial Epidermis: It forms the lower surface of the leaf. It is a single layer made up of parenchymatous cells.
Thin protective skin is located outside the surface of abaxial epidermis.
This layer has multicellular leaf hairs. The number of stomata are more than adaxial epidermis. This respiratory cavity is associated with other intercellular spaces
Mesophyll Tissue : The tissue between the upper and lower epidermis is called the mesophyll. It contains palisade, spongy tissue and vascular bundles.
Palisade Tissue : The adaxially placed palisade parenchyma is made up of elongated cells which are arranged vertically and parallel to each other. Intercellular spaces are negligible between them. Chloroplasts are present in large amount in cells.
The function of this tissue is of photosynthesis.
Spongy Tissue : These calls located on the upper side of abaxial layer are of irregular shape. Large intercellular spaces are located between the cells. So this issue is called spongy tissue. This tissue has less number of chloroplasts.
Vascular Bundles : Vascular bundles located in leaf are conjoints, collateral and closed. The structure of each vascular bundle is like vascular bundle of stem.
Due to reticulate venation present in sunflower leaf. In vascular bundle xylem, tissue is located towards adaxial epidermis and phloem tissue is located toward abaxial epidermis.
In longitudinally and transversely cut vascular bundle different thickenings are seen in the walls of the cells of xylem.
The size of vascular bundles are dependent on the size of veins.
The vascular bundles are surrounded by layer of thick walled bundle sheath cells.
In these leaves, various type of mesophyll tissue is located in adaxial epidermis and abaxial epidermis so leaves of dicotyledonous are called dorsiventral leaves.