Question

Explain the cohesion tension theory.

Answer 1

Most acceptable theory for the ascent of sap is the physical force theory, called as cohesion-transpiration pull theory. This theory was put forward by Dixon and Joly. According to this theory, the ascent of sap in plants is a physical process, the lifting force for which is provided by the pulling force generated by transpiration. The cohesion forces between the water molecules help in maintaining a continuous water column and the adhesion forces between water molecules and the tracheary elements help in sticking to water to the xylary elements. Both of these forces help in maintaining a continuous water column in the xylary elements.