Accordind to this theory:
-evaporation reduces the water potential of cells next to the xylem
-water enters these cells from the xylem which is at a higher water potential
-cohesive forces between the water molecules draw other water molecules up the xylem
-adhesive forces between the water molecules and the cellulose walls of the xylem vessel prevent the column of water from being pulled down by gravity and
-the pulling force results in water entering from the roots.