Describe the root pressure theory and its demerits.
Root pressure theory : The theory was put forward by Priestley (1916). Root pressure refers to positive hydrostatic pressure which is develops in xylem sap, when rate of water absorption is more than the rate of transpiration and as a result of which water is pushed up in tracheary element of root. Demerits of root pressure concept : (1) Magnitude of root pressure is maximum upto 2 atmosphere which can raise water upto 64ft. only. It can’t drive water in tall trees (300-400 feet) there is need of 20 atmosphere root pressure. (2) No root pressure in conifers. (3) Root pressure is low in summer when transpiration is high and high in spring when transpiration is low (4) Root pressure is not seen in rapidly transpiring plants.
