Capillary action is the name for the process that takes place when a paper towel soaks up a spilled liquid or when a plant transfers water from its roots to its leaves. Capillary action happens when water molecules are more attracted to the surface they travel along than to each other. In paper towels, the molecules move along tiny fibers. In plants, they move through narrow tubes that are actually called capillaries. Plants couldn’t survive without capillaries because they use the water to make their food.