Q.12:- Describe the internal structure of a dorsiventral leaf with the help of labeled diagrams.
Dorsiventral (Dicotyledonous) Leaf
There are three main parts in the leaf lamina of a dorsiventral leaf, viz. epidermis, mesophyll and vascular system.
Epidermis: The epidermis covers both the upper and lower surfaces. The upper epidermis is called adaxial epidermis, while the lower one is called abaxial epidermis. Cuticle is distinct. A higher number of stomata are present on the abaxial epidermis than on the adaxial epidermis. Stomata may be absent also in the adaxial epidermis.
Mesophyll: The tissue between the two epidermises is called mesophyll. The mesophyll is composed of parenchyma and contains chlorophyll. There are two types of cells in the mesophyll, viz. palisade parenchyma and spongy parenchyma. The palisade parenchyma is placed adaxially. It is made up of elongated cells; which are arranged vertically and parallel to each other. The spongy parenchyma is situated below the palisade parenchyma and extends to the lower epidermis. There are numerous large spaces and air cavities between the cells of spongy parenchyma.
Vascular Bundle: The vascular bundles can be seen in the veins and the midrib. Vascular bundles are surrounded by a layer of thick-walled bundle sheath cells. Vascular bundles are of different sizes because of reticulate venation.