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Related to mass flow: Mass flow hypothesis
mass flowan hypothesis to explain the movement of solutes in a plant by means of a hydrostatic pressure gradient. The idea is that in one part of the plant (the source) solute particles are actively secreted into sieve cells of PHLOEM, producing a high osmotic concentration which attracts water by OSMOSIS. In another part of the plant (the sink) solute particles are leaving the phloem, thus lowering the osmotic concentration which causes water to leave also. There is, therefore, a pressure gradient set up between the source (e.g. leaf) and the sink (e.g. root) and fluids flow from one to the other, down the gradient. See TRANSLOCATION (1).
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005