In order for the xylem sap to move under the action of root pressure, the plant needs ..

Due to root pressure, water and minerals are absorbed from the soil. Then, along the xylem, it rises to the ground part of the plant and enters the main photosynthetic tissue and other cells. But xylem sap, which consists mainly of water and inorganic substances, cannot continuously enter the plant. For movement to occur, excess water needs to leave the plant. This happens through special pores in the leaves. Water that was not used during photosynthesis evaporates and promotes thermoregulation.