Unidirectional movement of tracers along the stolon of Saxifraga sarmentosa.

When radioactive tracer is applied locally to the stolon of Saxifraga its long-distance movement after 18 hours is found to be strongly polarised; there is in addition a short-distance movement which is unpolarised. With caesium, the long-distance movement is predominantly in the phloem; with strontium in the xylem. These interpretations, a priori probable, were confirmed by artifically reversing, separately, the xylem and the phloem currents. With long pieces of excised stolon only the unpolarised short-distance movement is observed. These results constitute evidence against simultaneous bidirectional translocation in the same sieve tube, and are consistent with either the Münch or the electro-osmotic theory.