A number of theories have been proposed to explain the mechanism of ascent of sap from time to time. C Bose? Q.93 Pulsation theory to explain ascent of sap Desrnodium was proposed by :-(1) Dixon and Jolly (2) Curtis (3) J.C. Bose (4) None of these Show Answer. It has been estimated that the sap must flow through 230 to 400 pulsatory cells per second to account for the normal rate of ascent of sap. The conducting cells in xylem are typically non-living and include, in various groups of plants, vessels members and tracheids. Options (a) capillarity (b) pulsatory movement of living tissue (c) role of atmospheric pressure (d) transpiration pull and cohesion. It is based up on three basic assumptions which are cohesion in between water molecules, continuity of water column and transpiration pull. Root pressure forces the water up from below. Here are following theories which explain the ascent of sap in plants: a) Root pressure (b) Capillarity (c) Vital theory and (d) Cohesion-tension theory. Vital theories: Westermaier in the year 1883 for the first time suggested that living cells take part in ascent of sap. Explanation: Cohesion and transpiration pull theory was proposed by Dixon and Jolly in 1894. We are going to discuss briefly some of the important theories as follow: Theory of Vital Force. Theory # 2. Transpiration pull cohesion theory for ascent of sap in trees is most widely accepted. VITAL FORCE THEORY According to these theories the forces required for ascent Of sap are generated in living cells of plants. Munch hypothesis is based on a) Translocation of food due to TP gradient and imbibitions force Correct Answer: transpiration pull and cohesion. Here are following theories which explain the ascent of sap in plants: a) Root pressure (b) Capillarity (c) Vital theory and (d) Cohesion-tension theory. Root pressure forces the water up from below. It was a very controversial theory when first proposed (Böhm 1893; Dixon 1914, pp. So, the theory could not explain satisfactorily the mechanism of ascent of sap and thus discarded. (a) ROOT PRESSURE. According to him, the cells of this layer were expanding and contracting alternately. They are as follows: Vital theories. Root pressure theory. Ascent of Sap Mechanism. The ascent of sap in the xylem tissue of plants is the upward movement of water and minerals from the root to the crown. According to this theory, the ascent of sap is due to a hydrostatic pressure developed in the roots by the accumulation of absorbed water. Pulsation Theory of Bose: Bose observed that the pulsatory activity of the innermost layer of the cortex, just outside the endodermis is responsible for the ascent of sap. 1. Many theories have been proposed to explain the mechanism of ascent of sap. Xylem is a complex tissue consisting of living and non-living cells. The hydrostatic pressure generated in the root which forces the water upward in the stem is called root pressure. The opinions are piercingly divided as to what brings about upward movement of water in plants. The pressure developing in the tracheary elements of the xylem as a result of the metabolic activities of root is referred as root pressure.If a plant system is cut a few inches above its base, the xylem sap is seen flowing out through the cut end. But it was already estimated by Bose that for one pulsation it took a minimum of 14 seconds. a) Pulsation theory b) Transpiration Pull theory c) Root pressure theory d) Atmospheric pressure theory 2. (a) ROOT PRESSURE The hydrostatic pressure generated in the root which forces the water upward in the stem is called root pressure. vital force theory godlewski relay pump theory/ clanbering theory opposed by straus burger pulsation theory (j.c.bose) supported by molisch others did not suppored 8. 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