Leaf is a lateral and flattened structure borne at the node of the stem, bearing a bud in its axil. The leaves originate from shoot apical meristems and are arranged in an acropetal order. Each axillary bud later develops into a branch. The structure of leaf can be identified with its three distinct parts, namely, leaf base, petiole and lamina.

Leaf base:The leaf is attached to the stem by the leaf base bearing two lateral small leaf-like structures called stipules. The leaf base may extend to become sheath covering the leaf base in monocotyledonous plants or may become swollen (called pulvinus) in leguminous plants.

Petiole: The main function of petiole is to help hold the blade to light, for the leaves to perform photosynthesis. Petioles also allow the leaf to flutter in wind, thus bringing fresh air to leaf surface.

Lamina:The lamina is the green flattened part of the leaf comprising veins and veinlets. A middle thick, prominent vein is called as midrib. The purpose of veins is to maintain the rigidity of the lamina and also acts as a channel to transport water, mineral, food materials and wastes. The shape, margin, apex, surface and extent of incision of lamina vary from species to species.

Function of leaf:The leaf is the most essential vegetative organ for conducting photosynthesis due to the presence of green pigment called chlorophyll. The photosynthesis takes place in the presence of sunlight, water and carbon dioxide.

A.    Parts of a leaf                        B. Reticulate venation           C. Parallel venation

 

Venation:

Venation is defined as the arrangement of veins and veinlets in the lamina of a leaf. Venation is mainly of two types, reticulate and parallel. A network-like formation of veins is termed as reticulate venation. This type of venation is characteristic of dicotyledonous plants. When the veins run parallel to the midrib, then the arrangement is called as parallel venation. This type of venation is characteristic of monocotyledonous plants.