Course Overview
A leaf is a lateral developed flattened structure borne on the stem. It develops at the node and bears a bud in its axil. It originates from the shoot apical meristem and arranged in an acropetal order of the stem. Leaves are the most important vegetative organ for photosynthesis.
Parts of a leaf
A typical leaf consists of three parts :
(i) Leaf base :The lowermost (basal) part of the leaf by which the leaf is attached to the node of the stem is called leaf base. Leaf base may bear two (a pair) lateral small leaf like structures called stipules. In monocots, leaf base expands to form a sheath covering the stem wholly or partially. In some leguminous plants, the leaf base swells and is called pulvinus.
(ii) Petiole : The cylindrical stalk that joins the leaf base with the leaf blade (lamina) is called petiole. It holds the leaf blade above the level of the stem so as to provide sufficient light to the leaf. The long, thin, cylindrical, flexible petiole allows leaf blade to flutter in wind. It thus produces a cooling effect in the leaves by bringing fresh air to the leaf surface.
(iii) Lamina or leaf blade :: It is green expanded part of the leaf. The leaf blade is supported by the veins and veinlets. The prominent vein present in the middle of the leaf blade is called midrib. The veins provide rigidity and strength to the leaf blade and also act as a channel for transport of water, minerals and food material. The shape, margin, apex, surface and extent of incision of lamina varies in different leaves.