The Movement of Tracers along the Petiole of Nymphoides peltatum: I. A. PRELIMINARY STUDY WITH 137Cs

It is shown that the general postulate of a mass flow with lateralescape of tracer accounts fairly satisfactorily for the well-establishedexponential fall-off in tracer activity down the axis. The shapeof the curves relating the logarithm of the activity to distanceis concave upwards, and it is suggested on the assumption ofa mass-flow model that this is evidence either of an acceleratingvelocity down the petiole, or of a falling rate of lateral leakageout of the sieve tubes. It has also been shown that no satisfactoryestimate of the linear velocity of movement can be got fromthe usual type of tracer study without further information ofa kind not usually provided, and no estimate has proved possiblein the present case.