But none of the theories are free from criticisms. According to the vital force theory the conduction of water up the xylem vessel is a result of vital action of the living cells in the xylem tissue. Other theories except the new CP theory, do not advocate the contribution of living cells.
Jagadish Chandra Bose forwarded a mechanism for the ascent of sap in 1927. The electrical ‘pulsations’ or oscillations in electric potentials, which he found and proved that these were coupled with rhythmic movements in the telegraph plant Codariocalyx motorius (then Desmodium). On the basis of this Bose theorized that regular wave-like ‘pulsations’ in cell electric potential and turgor pressure were an endogenous form of cell signalling. According to him the living cells in the inner lining of the xylem tissue pumps the water by contractive and expulsive movements similar to the animal heart circulating blood. Though his considerations are similar to the most modern CP theory, but like the other three theories this theory has not been conclusively proved.
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