A Model of Mass Flow in the Phloem

Abstract

An analysis is made of the flow of sieve tube sap in the path region of a translocating plant. A model is presented which describes such flow and its applicability to several hypotheses of translocation mechanism is discussed. The physical characteristics to be expected of sap flow are considered including the concept of an optimum concentration of sugar. The special role which may be played by sucrose is examined and the possibility that translocation flow may have the dynamic characteristics expected of a compressible fluid is introduced. It is concluded that a Fick's law relationship will describe mass flow translocation very satisfactorily regardless of the mechanism of drive involved.