Xylem tissue extends from the roots of a plant, up the stem to the leaves and branches. The tissues are made of tracheids and vessel elements. Tracheids are a series of elongated cells that grow in tight bundles and then die, leaving hollow interconnected cell membranes. Water can pass from one tracheid to another through pits that are separated by extremely thin cell walls. Also, hollow vessels are formed from individual vessel elements. Vessel elements join end to end to form continuous hollow tube so water can pass easily. In smaller plants, osmotic pressure from water entering the roots by osmosis is sufficient to force water up through the hollow tracheids and vessel elements. However, in larger plants, osmotic pressure is not great enough to overcome the force of gravity. There is a combination of other forces to finish the transport. A lot of water is used by plants each day, from photosynthesis and evaporation. Evaporation of water from the leaves, called transpiration, causes the water content of the cells surrounding the vascular tissue to drop, and the osmotic pressure moves water out of the vascular tissue into the leaf. The movement of water in the leaves pulls water upwards through the vascular system all the way from the roots. This occurs because of water’s cohesive and adhesive properties, as well as tension. The pull or tension generated in the leaves applies a force to water in the vascular system. The strong cohesion (attraction to each other because of hydrogen bonding) of water molecules transmits the force throughout the vascular system. If the top water molecule is pulled, because of cohesion, the rest of the water molecules will follow. When tension and cohesion are combined with adhesion (attraction to other molecules), the attraction of water for the walls of the xylem vessels, enough combined force is produced to left the water. The combined forces of cohesion and adhesion is called capillary action. The smaller the...