Final answer:
Capillary action in plants is primarily caused by the forces of cohesion, which is the attraction between water molecules, and adhesion, the attraction between water molecules and plant tissues. These forces enable water to rise against gravity through a plant's xylem.
Step-by-step explanation:
Capillary action, which draws water up a plant against gravity, is caused by both cohesion and adhesion. Cohesion refers to the attraction between water molecules, which helps in the movement of water up from the roots of plants towards the leaves. Adhesion, on the other hand, is the attraction between water molecules and the molecules of the plant tissues, such as the xylem, a factor crucial for the ascent of water inside the plant. These forces work in conjunction to overcome gravity and allow water to travel upwards through the narrow tubes within plants, a process essential for plant hydration and nutrient transport.