PRELIMINARY STUDIES ON SAPFLOW IN COCOS NUCIFERA L. II. PHLOEM TRANSPORT

Abstract

Techniques are described which enable the transport of phloem sap in the coconut to be studied with greater precision than previously. Factors governing the flow of sap include manipulation and damage to the tissue, which tend to reduce the flow, whilst the use of sharp knives to slice the phloem enhances exudation. A possible role for manipulation is proposed, but it does not seem essential for the induction of exudation. Phloem sap pressures have been measured directly up to about 7.6 bar, agreeing with those that might be expected from measurements of the osmotic pressure of the phloem sap and the water potential of the xylem sap. Very high rates of specific mass transfer (SMT) have been measured for phloem and sieve tubes, supporting earlier estimates on Arenga, and tentative measurements have been made of the hydraulic conductivity of Cocos sieve tubes. In general, the observations support the view that mass flow through the phloem may be driven osmotically, but the remarkable facility with which the solute content of the sieve tubes can be altered, will make proof difficult. Implications of the work in relation to the transmission of phloem‐borne pathogens are discussed. Copyright © 1977, Wiley Blackwell. All rights reserved