The cohesion-tension theory, also known as suction force theory, states that water is able to move up the stem xylem due to the strong attraction of water molecules to each other. The absorption of water from cut ends of stems disproves the root-pressure theory which states that all plant roots absorb excess of water by an active process and builds up a hydrostatic pressure within the root system, called root pressure. This activity pushes the water upwards all along the length of the stem.