Anatomy of a Dicot and Monocot Leaves
Leaves are very important vegetative organs. They are mainly concerned with photosynthesis and transpiration. Like stem and roots, leaves also have the three tissue system – dermal, ground and vascular. The dermal tissue system consists of an upper and lower epidermis. The ground tissue system that lies between the epidermal layers of leaf is known as mesophyll tissue. Often it is differentiated into palisade parenchyma on the adaxial (upper) side and spongy parenchyma on the abaxial (lower) side.
In dorsiventral leaves the mesophyll is differentiated into palisade and spongy parenchyma, the former occurring on the upper side and the later on the lower side Example: Sunflower. In isobilateral leaf palisade is present on both sides of the leaf and inbetween them spongy parenchyma is present. Example: Nerium. In some plants Example: Ficus calcium crystals are present. There are also leaves where spongy tissue alone is present in some epidermal cells Example: Grasses.
The presence of air spaces is a special feature of spongy cells. They facilitate the gaseous exchange between the internal photosynthetic tissue (mesophyll) and the external atmosphere through the stomata.
The vascular tissue system is composed of vascular bundles. They are collateral and closed. The vascular tissues forms the skeleton of the leaf and are known as veins. The veins supply water and minerals to the photosynthetic tissue. Thus the morphological and anatomical features of the leaf help in its physiological functions.