EVERYDAY SCIENCE

Detailed explanation-1: -The theory of ascent of sap given by Dixon and Jolly is also called the ‘Cohesion-tension theory’. According to this theory, loss of water from aerial parts of the plants creates a suction force in the xylem. This pulls up water from the roots.

Detailed explanation-2: -Henry H. Dixon, an Irish botanist, and John Joly, a physicist, in 1894 developed the idea of cohesion-tension mechanism of ascent of sap.

Detailed explanation-3: -Hint: The ‘Dixon-Jolly’ hypothesis was introduced in 1894 by Dixon and Jolly. According to this theory, water molecules are in constant motion and are strongly attracted to one another, forming a continuous column of water xylem elements, with water being drawn upwards by transpiration.

Detailed explanation-4: -Transpiration pull is the most widely accepted theory for the ascent of sap from roots to the shoot system. It is also called the cohesion tension theory. This mechanism was proposed by Dixon and Jolly in 1894. Tension or negative pressure in the water column of xylem channels results in this upward pull.

Detailed explanation-5: -Dixon and Jolly (1894) proposed cohesion and adhesion theory. According to the theory a strong cohesive force between the water molecules is responsible for the tensile strength of water column in vessels of conducting tissue xylem.