Phloem Physiology and Protective Sealing Mechanisms

Abstract

RECENTLY Dr Spanner, in a review “Transport in the Phloem”¹, described certain aspects of my work² but reinterpreted my reported observations in accordance with his scheme to explain the mechanism of phloem transport. His description that the massage pretreatment applied to Ricinus stems in my experiments was “gentle” is not correct. The theory behind the method is to compress phloem sieve tubes containing sap under pressure of about 10 bar, so as to make it surge rapidly along the tubes; manual pressure was applied firmly though not so as to produce detectable damage during the application. Similarly the brief application of quite strong pressure is needed to stop exudation completely.