Solution: Root pressure is developed in plant roots due to active nutrient absorption from the soil. Water (together with minerals) increases the pressure in the xylem when nutrients are actively absorbed by root hairs. The water is pushed up to small heights by this pressure. Root pressure can be observed experimentally by cutting the stem of a well-watered plant on a humid day. When the stem is cut, the solution oozes from the cut end. Hence, Root pressure aids plant upward mobility in herbaceous plants.