The vertical section of a dorsiventral leaf through the lamina shows three main parts, namely epidermis, mesophyll and vascular system. The epidermis which covers both the upper surface and lower surface of the leaf has a conspicuous cuticle. The abaxial epidermis generally bears more stomata than the adaxial epidermis. The latter may even lack somata. The tissue between the upper and the lower epidermis is called the mesophyll.
Mesophyll, which possesses chloroplasts and carry out photosynthesis, is made up of parenchyma. It has two types of cells – the palisade parenchyma and the spongy parenchyma. The adaxially placed palisade parenchyma is made up of elongated cells, which are arranged vertically and parallel to each other. The oval or round and loosely arranged spongy parenchyma is situated below the palisade cells and exter ds to the lower epidermis.
There are numerous large spaces and air cavities between these cells. The vascular system includes vascular bundles, which can be seen in the veins and the midrib. The size of the vascular bundles are dependent on the size of the veins. The veins vary in thickness in the reticulate venation of the dicot leaves. The vascular bundles are surrounded by a layer of thick-walled bundle sheath cells.
