Transpiration occurs through the stomata. The stomata are primarily meant for absorption of CO2, but the water vapors also escape through stomata and cause transpiration. Thus transpiration is called as a necessary evil because it is an inevitable process. The loss of water can lead to wilting, serious desiccation, and shortage of water. Transpiration helps in the ascent of the sap and the pulling of the water from the roots to the tips. Thus is it considered to be a necessary evil.
