Cambridge Encyclopedia » Cambridge Encyclopedia Vol. 45

leaf - Leaf anatomy, Leaf morphology, Leaf terminology, Adaptations

water leaves plants stomata

The main photosynthetic organ of green plants, divided into a blade (lamina) and a stalk (petiole). The lamina is usually broad and thin, to present maximum surface area to sunlight and allow easy diffusion of gases and water vapour to and from the leaf. It is composed of several distinct layers of tissues: the epidermis protects the inner tissues - the palisade layer, which is the primary site of photosynthesis, and the spongy mesophyll, which has large air spaces and is the primary site of gas exchange. A network of vascular tissue, the veins, transports water and sap to and from the leaf. The epidermis secretes a waxy cuticle, mostly impervious to water and gases which enter and leave via pores (stomata) concentrated in the lower surface of the leaf. The main source of water loss for a plant is due to transpiration via the leaves. This is minimized by the waxy cuticle, and by the opening and closing of the stomata in response to changes in humidity. Other modifications to reduce water-loss are found particularly in plants from dry or cold regions, including reduction in leaf size, inrolled margins to protect stomata, and regular shedding of leaves during unfavourable seasons. Some plants have replaced their leaves entirely with less vulnerable photosynthetic organs, such as green stems. Leaves range from a few mm to 20 m/65 ft in length, exhibit a great variety of shapes, and may be entire, toothed, lobed, or completely divided into separate leaflets. These characters and the arrangement of the leaves on the stem are diagnostic for many plant groups. Leaves may also have specialized functions, such as water-storage in succulents, traps in carnivorous plants, and tendrils in climbers.

User Comments

Your email address will be altered so spam harvesting bots can't read it easily.
Hide my email completely instead?

Cancel or