The stomata are primarily meant for absorption of CO2 but these also help in exchange of gases, but at the same time water vapors also escape through stomata. Thus transpiration is described as necessary evil because it is an inevitable process but potentially harmful. Loss of water can lead to wilting, serious desiccation, and often death of a plant, if there is shortage of water. There is good evidence that even mild water stress results in reduced growth rate, and reduction in yield.