Cohesion and Transpiration Pull Theory : 

This theory was first proposed by Dixon and Jolly (1894) and is based on the following features :

(i) Cohesion and Adhesion : Mutual attraction between water molecules is called cohesion. The walls of tracheids and vessels of xylem are made-up of lignin and cellulose and have stomg affinity for water (adhesion).

(ii) Tension : Transpiration pull develops a negative pressure or tension in xylem sap which is transmitted down to the root.

The moist walls of mesophyll cells in leaf lose water vapour to the intercellular spaces. Sufficient quantity of water is transpired through intercellular spaces of the mesophyll cells through stomata. This is because, dry air outside the leaf has lower water potential than moist air of leaf, as a result water diffuses out of stomata and diffusion pressure deficit (DPD) increases. As a result, more water is sucked from adjoining inner mesophyll . cells and ultimately from xylem tissue. This tension is transmitted down to the roots.

The water column does not break because of cohesive and adhesive forces.