Leaf - Introduction

Description:

Leaf is the lateral flattened structure borne on the stem. They develop at the node and bears a bud in the axil.

Occasionally they can be needle like or scale like. At the top of the stem, there is a mass of the meristematic cells which divide frequently and are called the shoot meristem. Leaves originate from the shoot meristem as leaf primordia, and gradually enlarge.

Parts of a leaf

A typical leaf consists of 3 main parts −

Leaf Base

• Point of attachment of the leaf to the stem.
• It bears two lateral small leaf like structures called stipules.
• In monocots the leaf base expands into a sheath covering the stem partially or wholly.
• Some leguminous plants may have swollen leaf base called pulvinus.

Petiole

• Help to hold the blade to light.
• Long thin flexible petiole allow leaf to flutter in the wind which helps in cooling and brings fresh air to leaf surface.

Lamina

• Also called the leaf blade.
• It is the green expanded part of the leaf with veins and veinlets.
• It is flat, thin and broad.
• Usually have a prominent vein at the middle called the midrib.
• The shape, margin, surface vary in different leaves.