Ascent of sap is the upward movement of water in a plant from root tip to plant body. This mechanism is explained by various theories. One of the first one of these was pump theory which was later modified to pulsation theory. These theories assumes that water moves upwards from root by pumping action of living cells which pump water similar to pumping of heart. Here the dead xylem tissues act as reservoirs. This theory was first put forward by Westermeir (1880). And was justified by Godlewski, J.C.Bose (1920), and Priestly.

J.C. Bose's Pulsation Theory for Ascent of Sap

Jagadish Chandra Bose, an eminent Indian scientist, proposed the theory of pulsation for the ascent of sap in plants. This theory challenged the prevailing beliefs at that time and provided a new perspective on how water and nutrients move upwards in plants.

Background:
Before Bose's theory, there were three popular theories to explain the ascent of sap in plants:
1. Relay pump theory: This theory suggested that the ascent of sap is achieved through a series of pumps located at different levels in the plant.
2. Transpiration pull theory: According to this theory, the evaporation of water from the leaves creates a negative pressure or tension, which pulls the sap upwards.
3. Root pressure theory: This theory proposed that the roots actively pump water into the xylem, creating a positive pressure that pushes the sap upwards.

Bose's Pulsation Theory:
J.C. Bose's theory of pulsation challenged these existing theories. According to him, the ascent of sap is not due to a continuous flow of water but rather a rhythmic pulsation of sap in the xylem vessels. Here is an explanation of Bose's theory:

1. Rhythmic pulsation: Bose observed that the sap in the xylem vessels of plants exhibited rhythmic pulsations, similar to the human heartbeat. These pulsations were measurable and could be detected using his specially designed instruments.

2. Oscillatory movements: Bose suggested that the ascent of sap occurs due to the oscillatory movements of water molecules within the xylem vessels. He hypothesized that these movements are caused by the alternating expansion and contraction of the living cells surrounding the vessels.

3. Physical phenomenon: Bose believed that the pulsation of sap is a physical phenomenon, similar to the movement of fluids in narrow tubes. He compared the xylem vessels to capillary tubes and proposed that the pulsations are driven by the physical properties of water and the forces acting on it.

4. Role of living cells: Bose emphasized the importance of living cells surrounding the xylem vessels in generating the pulsations. He suggested that these cells expand and contract rhythmically, creating pressure changes that drive the movement of sap.

5. Supporting evidence: Bose conducted several experiments to support his theory. He used his instruments to measure the pulsations, studied the effect of external factors on the pulsations, and compared the pulsation patterns in different plant species.

Conclusion:
J.C. Bose's pulsation theory proposed a new explanation for the ascent of sap in plants. Although his theory was not widely accepted at that time, it contributed to our understanding of plant physiology and challenged the prevailing beliefs about how water and nutrients move in plants.