Water is a polar molecule. The hydrogen atoms are partially positive and the oxygen end is partially negative. This causes water molecules to be attracted to eachother. This attraction to other polar molecules and to water molecules being attracted to eachother is part of hydrogen bonding. Since water molecules stay close to one another, this is called cohesion, and even though the bonds between water molecules continually break, new ones form. Adhesion is the tendency of different particles or surfaces to cling to one another. This allows transport of water molecules up through the xylem tubes, which are part of the vascular tissues in a plant's veins. The primary force that creates capillary action which is movement of water up through small tubes(xylem) is the adhesion between the water and the surface of the xylem walls. Therefore, the attraction of water molecules to other water molecules, keeps them together and the adhesion of those water molecules to the walls of the xylem, help to transport water up from the roots to the leaves of a plants, via capillary action. As water exits the plant by transpiration from the pores inside its leaves, more water can move up from the soil into the xylem tubes inside the plant's roots.