- Vital theory
One of the four theories proposing a mechanism for the ascent of sap through the
xylem tissue of thevascular bundle of plants. Other theories areroot pressure theory ,cohesion-tension theory andCP theory .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 thexylem tissue. Other theories except the new CP theory, do not advocate the contribution of living cells.Jagadish Chandra Bose forwarded a mechanism for theascent of sap in1927 . 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 cellelectric potential andturgor pressure were anendogenous 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 animalheart circulatingblood . Though his considerations are similar to the most modern CP theory, but like the other three theories this theory has not been conclusively proved.See also
*
Cohesion-tension theory
*Root pressure theory
*CP theory External links
* [http://www.ias.ac.in/currsci/jul10/articles33.htm]
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