The Movement of Tracers along the Petiole ofNymphoides peltatum: I. A. PRELIMINARY STUDY WITH137Cs

Abstract

It is shown that the general postulate of a mass flow with lateral escape of tracer accounts fairly satisfactorily for the well-established exponential fall-off in tracer activity down the axis. The shape of the curves relating the logarithm of the activity to distance is concave upwards, and it is suggested on the assumption of a mass-flow model that this is evidence either of an accelerating velocity down the petiole, or of a falling rate of lateral leakage out of the sieve tubes. It has also been shown that no satisfactory estimate of the linear velocity of movement can be got from the usual type of tracer study without further information of a kind not usually provided, and no estimate has proved possible in the present case.