Leaf is the principal appendage or lateral organ of the plant. Leaf, both morphologically and anatomically, is the most variable plant organ. The foliage leaves are normal leaves, which are more in number and are concerned with photosynthesis, gaseous exchange and transpiration. Their internal structure and tissue arrangement exhibit a great deal of variation.
On the basis of anatomical features, foliage leaves can be differentiated into two major types dorsiventral leaf and isobilateral leaf.
Dorsiventral leaves are bifacial leaves having an upper surface (also .called ventral surface or adaxial side) facing towards sky sun and a lower surface (also called dorsal side or abaxial side) facing towards ground. Upper surface is more illuminated than the lower surface. Isobilateral leaves are not distinguished into such upper and lower surface. Both the surfaces are almost equally illuminated due to their orientation.
Leaves, like other organs, are anatomically composed of three tissue systems-dermal tissue system, ground tissue system and vascular tissues system. The ground tissue in leaf is called the mesophyll. Mesophyll cells are of two types: palisade parenchyma and spongy parenchyma. Vascular tissue system includes the vascular bundles, which are mostly collateral and closed.