5.3 The Leaf

The leaf is a lateral, generally flattened structure borne on the stem. It develops at the node and has a bud in its axil. The axillary bud later develops into a branch. Leaves originate from shoot apical meristems and are arranged in an acropetal order. Leaves are the most important vegetative organs for photosynthesis. A leaf has three main parts: leaf base, petiole and lamina. The leaf is attached to the stem by the leaf base and may bear two lateral small leaf like structures called stipules. In monocotyledons, the leaf base expands into a sheath covering the stem partially or wholly. In  leguminous plants the leafbase may become swollen, which is called the pulvinus. The petiole help hold the blade to light. Long thin flexible petioles allow leaf blades to flutter in wind, thereby cooling the leaf and bringing fresh air to leaf surface. The lamina or the leaf blade is the green expanded part of the leaf with veins and veinlets. There is a middle prominent vein, which is known as the midrib. Veins provide rigidity to the leaf blade and transport water, minerals and food materials. The shape, margin, apex, surface and extent of incision of lamina varies in different leaves.

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