Transpiration

Transpiration:
Transpiration is define as the loss of water vapors from the internal tissue of living plants through the aerial parts such as leaves, green stem, lenticels etc under the influence of sunlight. Only about 1% of the water absorbed by terrestrial plants is used in metabolic reactions and most of it is lost by transpiration leaves.

Types of transpiration:
Transpiration in plants may occur through stomata, lenticel or cuticle and accordingly it is called stomatal, lenticular or cuticular transpiration. 

1. Cuticular transpiration: The surface of leaves and very often stems are covered by a waxy coating called cuticle which is actually a layer that is supposed to prevent loss of water. That is why in plants exposed to sunlight, the deposition of cuticles is heavy, while in plants of the shaded area, it is thin. However, water still evaporates through the cuticle and it is known as cuticular transpiration. Commonly 3-10% of transpiration takes place by this method. But in herbaceous shade-loving plants, it occurs up to 50% of total transpiration.
2. Lenticular transpiration: In woody plants, after the secondary growth the epidermis is replaced by periderm whose outer layer is composed of dead cells (cork). Inorder to provide aeration to the inner living tissues, at certain places the cork tissue opens out and forms small slits called lenticels. Transpiration taking place through lenticels is called lenticular transpiration. In comparison with other types of transpiration, this is very significant as it amounts to only 0.1% of the total.
3. Stomatal transpiration: Stomata are tiny pores found in the epidermis of leaves and young stems. They are meant for the gaseous exchange and the main source of transpiration. Loss of water vapors through microscopic pores surrounded by specialized guard cell is called stomatal transpiration. The process of transpiration is more rapid during the day than the night. It is because of the closing of the stomata during the night. It is because of the closing of the stomata during the night. About 80-95% of total transpiration takes place by stomata.

Advantages of transpiration

• The excessive water of the plant is transpired to the atmosphere from the aerial parts of the plants. 
• Transpiration causes cooling of the leaf and the plant as a whole. So, the plant stands in the bright sunlight. 
• With the increase of transpiration, the rate of absorption of water and minerals also increases. 
• The leaf temperature is maintained because of transpiration.