How does ascent of sap occur in tall trees ?

The cohesion-tension-transpiration pull model explains the ascent of sap in tall trees.
* It was proposed by Dixon.
* Ascent of sap depends mainly on the following physical properties of water.
* Cohesion, Adhesion Forces.
* These properties give water high tensile strength and high capillarity.
* In plants, capillarity is aided by the small diameter of the tracheiary elements – the tracheids and vessels.
* Transpiration pull is the driving force for upward movement of water.
* Measurements reveal that the forces generated by transpiration can create pressures sufficient to lift a xylem sized column of water over 130 meters high.