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

Internal structure of the leaf of a dicotyledonous plant: Epidermis:Upper and lower surfaces of the leaf are bound by the epidermis, known as the lower and upper epidermis respectively. The upper epidermis generally comprises of a single layer of cells. A thick cuticle is usually present on the outer walls of these cells. The stomata are absent and if present, they are few in number when compared to those on the lower epidermis. The lower epidermis is also made up of a single layer of cells bearing a large number of stomata and this is covered by a thin layer of cuticle. Each stoma is surrounded by two guard cells, which contains chloroplasts and opens into a large space below, called the sub-stomatal chamber. On account of the presence of chloroplasts, they are able to carry out photosynthesis to a limited extent.Mesophyll:The tissue between the upper and lower epidermis is called the mesophyll. The mesophyll consists of two regions - the palisade parenchyma and the spongy parenchyma. The palisade parenchyma is vertically elongated cells, which may be organised into one or more layers. The palisade cells are compactly arranged through out and show only little intercellular spaces. They process abundant chloroplasts. The palisade cells carry out photosynthesis in the presence of sunlight. The spongy parenchyma is components of the remaining portions of the mesophyll tissue, which is extended from below the palisade layer to the lower epidermis. Its cells are oval or rounded, enclosing numerous large air spaces and air cavities. These spaces open towards the outside through the stomata and help in the diffusion of gases. Spongy parenchyma cells contain chloroplasts to perform photosynthesis, like those of the palisade parenchyma.Vascular bundles:The vascular bundles are conjoint, collateral and endarch. Each vascular bundle is surrounded by a layer of thick-walled cells arranged compactly and is known as the bundle sheath. The xylem is situated towards the upper epidermis and the phloem lies towards the lower epidermis.