In this activity we take two capillary tubes of different diameters and place them in a beaker of coloured water as shown. We see that the water rises in both the tubes and that the narrower tube has a higher level of water. As water adheres to glass, the water molecules near the glass walls climb up the glass surface due to adhesion. In this process they also carry up the water molecules that are away from the walls due to surface tension and a small amount of water rises in the capillary tube, forming a concave meniscus. The height to which the water rises depends on the diameter of the tube. In plants, the water is absorbed by the roots and rises up the trunk due to capillary action.