We know the importance of leaves for a plant. They are the food producers that are responsible for the growth and survival of plants. Though leaves are seen in different shapes and sizes, yet their role remains the same. They carry out photosynthesis when there is enough sunlight and eventually shed when they can no longer make food. For instance, when they grow in the plant in such a position that is completely shut off from sunlight all through the time, they shed off. This process is called self-pruning in trees.
A broad leaf’s topmost layer has a thin waterproof coating called cuticle. Then there is a layer of transparent cells called epidermis. Beneath the epidermis are tightly packed cells containing lots of chlorophyll containing bodies called chloroplasts. This layer containing chloroplasts is called palisade layer. Under this palisade layer there is a spongy layer which contains loosely arranged cells. These cells allow the free movement of gases and water inside and outside the leaves. There are tissues located in the spongy layer called veins. These veins are the distributors of water and food throughout the plant.
Needle like leaves of a coniferous tree has a different structure from that of a broad leaf structure. The outside of the needle like leaves is harder and waxier, cutting down on water loss.
Leaves may grow opposite one another or alternately. They may be classified as those with petiole (that which connects leaf to the stem) and without one. Apart from their different shapes and sizes, leaves can also be classified as simple and compound leaves. A simple leaf has a single blade. Compound leaves are lots of smaller leaflets attached to a central stem which is itself attached to a twig.