What is capillarity? How this phenomenon is chemically explained? What is the relevance of capillarity for water transport in plants?

Capillarity is the phenomenon by which water moves inside extremely thin tubes (capillaries) aided by the attraction among water molecules and the capillary wall. The capillarity phenomenon is possible because water is a polar molecule and forms intermolecular hydrogen bonds. Thus there is electrical attraction (adhesion force) among the capillary wall and the water molecules that then pull each other (cohesion force) as they are bound. Not just water but other liquids may move inside capillaries by capillarity.

Capillarity is not too relevant for the transport of water in plants. It contributes only to a few centimeters of ascension.