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

Explanation

Dorsiventral leaves are found in dicot plants. These are generally horizontal and sunlight falls on the upper surface (i.e., ventral or adaxial surface). It comparises follow structures in its T.S.
(i) Upper epidermis: It is generally single layered outermost covering, consists of parenchymatous cells but sometime multilayered cuticle is well developed on upper epidermis. Epidermal cells lack chloroplast. It lacks stomata usually
(ii) Lower epidermis : It is just like upper epidermis but here stomata are present. Chloroplast is also absent but present in guard cell only.
(iii) Mesophyll: In between upper an lower epidemis there is mesophyll tissue which is divided into two regions.
(a)(a) Palisade parenchyma : These are elongated columnar cells without intercellular spaces. These have chloroplast in them. These cells are generally arranged in two layers.
(b) Spongy parenchyma : It is found below palisade parenchma. It consists of spherical or oval cells with intercellular spaces. Number of chloroplasts are more in palisade than spongy parenchyma. Intercellular spaces found in the spongy parenchyma are connected to sub-stomatal cavity. So stomata help in gaseous exchange.
(iv) Vascular bundles : Vascular bundles are found scattered in spongy parenchyma. The V.S, in midrib region is the largest. Vascular bundles are conjoint, collateral and closed type. Each vascular bundle is surrounded by a bundle sheath. In these bundles xylem is present towards the upper epidermis. While phloem is present towards lower epidermis. On both sides of the largest vascular bundle, there is prarenchymatous or collenchymatous mass of cells which lack chloroplast.