Bulk flow of xylem sap.

Water vapor exits the leaf via stomata by a process called transpiration.

Transpiration produces negative pressure (tension) that pulls the water in the xylem into the leaf.

Water molecules in the xylem form a continuous column by cohesion among water molecules and adhesion of water molecules to cellulose.

The transpirational pull is transmitted from the leaves to the root to facilitate uptake of water from the soil.