Most accepted theory for the ascent of sap is
Most accepted theory for the ascent of sap is
The correct option is A transpiration pull theory
Transpiration pull is the tension which develops due to transpiration. It has been demonstrated that the rate of water absorption and hence, the ascent of sap closely follows the rate of transpiration. Cohesion and transpiration pull theory, given by Dixon and Jolly (1894) is the most accepted theory of the ascent of sap.
Root pressure theory (Priesty, 1916) is about active water absorption. It was not found to be applicable to all the plants (e.g. gymnospermous tallest trees). Moreover, this pressure is low to raise the sap to the top of trees and also many reasons which this theory was unable to prove.
Pulsation theory or vital force theory (J C Bose, 1923) was also discarded because the living cells do not seem to be involved in the ascent of sap as water continues to rise upward in the plant in which roots have been cut or when the living cells of stem are killed by poison and heat (Stress burger, 1891)
Capillary theory (Bohn; 1863), laid stress on capillarity movement of water due to adhesion and cohesion forces balanced by the downward pull of gravity, it was also discarded, as the capillary movement is too slow and applicable only to small sized plants and tall plants with narrow vessels.
transpiration pull theory
Transpiration pull is the tension which develops due to transpiration. It has been demonstrated that the rate of water absorption and hence, the ascent of sap closely follows the rate of transpiration. Cohesion and transpiration pull theory, given by Dixon and Jolly (1894) is the most accepted theory of the ascent of sap.
Root pressure theory (Priesty, 1916) is about active water absorption. It was not found to be applicable to all the plants (e.g. gymnospermous tallest trees). Moreover, this pressure is low to raise the sap to the top of trees and also many reasons which this theory was unable to prove.
Pulsation theory or vital force theory (J C Bose, 1923) was also discarded because the living cells do not seem to be involved in the ascent of sap as water continues to rise upward in the plant in which roots have been cut or when the living cells of stem are killed by poison and heat (Stress burger, 1891)
Capillary theory (Bohn; 1863), laid stress on capillarity movement of water due to adhesion and cohesion forces balanced by the downward pull of gravity, it was also discarded, as the capillary movement is too slow and applicable only to small sized plants and tall plants with narrow vessels.
