A typical leaf consists of different parts, having the different characteristics and functions. Study of those different parts is very easy to say as the anatomy of leaf. The outer surface of the leaf has a thin waxy covering called the cuticle, this layer's primary function is to prevent water loss within the leaf. Directly underneath the cuticle is a layer of cells called the epidermis. The vascular tissue, xylem and phloem are found within the veins of the leaf. Veins are actually extensions that run from to tips of the roots all the way up to the edges of the leaves. The outer layer of the vein is made of cells called bundle sheath cells and they create a circle around the xylem and the phloem. Let us go for the discussion about the parts of the leaf as follows:
LEAF BASE OR HYPOPODIUM
The base of the lamina represents the hypopodium at the anatomy of leaf. It has the following Characteristics:
The stretched area at the base of the petiole represents the leaf base. It represents the area of attachment between the lamina and the main stem. The upper part of the leaf base represents the leaf axil, which may bear the axillary buds. The stipules arise from this area. The leaf base may be swollen forming a cushion-like structure called pulvinus, example: mango leaf. Sometimes the cells of the pulvinus may be swollen, consisting of turgid cells giving mechanical support to the plant, example: Mimosa pudica. Whenever touched, the pulvinus lose water and the plant droops down, due to seismonastic activity. In monocot plants, the leaf bases are stretched, forming a sheath-like structure, clasping around the stem, which is called sheathing leaf base ; example: paddy leaf.
The hypopodium helps in the fixation of the leaves to the stem. It gives protection to the stem in the form of sheathing leaf base. It helps to storage of water in the pulvinus.
LEAF STALK OR PETIOLE OR MESOPODIUM
The short stalk connecting the lamina and leaf base is called petiole in the anatomy of leaf. It has the following Characteristics:
The stalk is cylindrical, stout but non-woody in nature and it can be long, short or sometimes absent. It attaches the lamina to the leaf base. There are some leaves without petiole and they are called sessile leaves, such as poppy. It lies in the same plane as with the lamina axis. Majority of the leaves are with petiole and are called petiolate leaves such as Ficus, Hibiscus etc. Sometimes the petiole is attached to the ventral surface of the lamina at right angles, and it is called the peltate leaf.
It supports the lamina and attaches it to the main stem and it spreads the lamina to the environment to receive light for photosynthesis. It forms the leaf axil and gives the space for axillary bud and it also conducts food and water for the tree.
LEAF BLADE OR LAMINA OR EPIPODIUM
In the anatomy of leaf the flat lateral portion of the leaf enriched in chlorophyll, helping in photosynthesis is called lamina or leaf blade. It also named as epipodium. It has the following Characteristics:
It is mostly green in color due to the presence of chlorophyll, but sometimes may appear multicolored due to the presence of other pigments. It is the flattened, expanded, terminal portion of the leaf. It has a fine network of veins, which may be reticulate or parallel in nature. In most of the leaves there is a distinct mid-rib, that runs distinctly through the middle of the lamina from base to apex. The petiole usually is a prolongation of the mid-rib at the base of the lamina. The apical part of the lamina forms the leaf-apex. In anatomy of leaf it is clear that the lateral sides of the lamina form the leaf margin. The lamina has two faces, the upper face or the dorsal face or the adaxial surface is deep green in color, due to the presence of more density of chlorophyll, while the lower surface or the ventral surface or the abaxial surface is grass-green in color due to less chlorophyll concentration. The differences in the dorsal and ventral surfaces are distinctly observed in the dorsiventral leaf Such as leaves like mango, Cucurbita etc. If the two surfaces are identical or similar in nature, they are isobilateral leaves e.g. Monocot leaves of rice, wheat, maize etc. If any of the parts of the leaves are lacking the leaves are said to be incomplete such as Agave.
As per anatomy of leaf the lamina is the principal site for photosynthesis. The venation forms the framework or the basic skeleton of the leaf blade. The thick cuticle formed of cutin protects the lamina.The veins help in conduction of water and translocation of food in the leaf tissues. The presence of stomata helps in gaseous exchange and loss of excess water in the form of water vapour by transpiration.