Question

Why is transpiration considered necessary evil?

Answer 1

Transpiration is tehprocess of evaporation of water from leaf surface , through stomatal openings.
Its said to be evil , because it causes loss of water from plants. In arid regions this loss of water may cause dessication in plants , water stress as well. But its also necessary and unavoidable. Because it causes cooling in plants, apart from that transpiration creates a transpirational pull , that causes the roots to absorn more and more water from soil. This is of major significant because when water is abosrbed , many important minerals dissolved in water that are required for plant growth are also absorbed alongwith water.
Transpiration also playes major role in water cycle in nature, that is responsible for precipitation ( rains).

Thats why this process is evil yet necessary .