why transpiration is necessary evil

The loss of water in the form of vapours from the living tissues of aerial parts of the plant is termed as transpiration.  

• It helps for the upward movement of water or sap from root to leaves. Transpiration prevents it by removing the extra water.
• It reduces the metabolic heat by acting as a coolant.
• It distributes the nutrients to all parts of the body.
• It indirectly helps for the intake of salt.

It helps plants in many ways and that is why,transpiration is termed as 'necessary evil ' for the plant growth.