The leaves perform three main functions such as manufacture of food, interchange of gases between the atmosphere and the plant body and evaporation of water. Some of the functions are described below. The functions of modified leaves are not dealt as they carryon specialised functions as discussed earlier.
A. Manufacture of food
It is the primary function of green leaves. The process is called photosynthesis by which leaf manufactures food material in the presence of sunlight and green pigment- chlorophyll present in the leaf. The preparation of food material takes place out of water and carbon dioxide obtained from the soil and the air respectively.
B. Interchange of gases
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It takes place both for respiration and photosynthesis. There are numerous, minute openings present on the leaves, called stomata, through which gaseous exchange takes place between the atmosphere and the plant body.
C. Evaporation of water
Water absorbed by the root hairs of the plant is evaporated from the leaf surface during the day time. It generally takes place through the stomatal openings. The phenomenon is known as transpiration. This process allows the plant to absorb water and minerals from the soil and conduct the same to the top of the plant.
D. Storage of food
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Fleshy leaves of Indian aloe, Portulaca and fleshy scale leaves of onion store food materials and water for the future of the plants. Fleshy and succulent leaves of xerophytic plants growing in desert area always store a huge quantity of water, mucilage and food materials.
E. Vegetative propagation
Leaves of Bryophyllum, Begonia and Kalanchoe produce buds by means of which they give rise to new plants by vegetative propagation. In these cases when leaf lamina touches the ground, the leaf margin at point produces roots and form a bud that grows into a new plant.