SUBAQUEOUS TRANSPIRATION IN NEW PERSPECTIVE

S ummary Dixon's original observation that the submerged shoots of terrestrial plants continue to take up water through the cut stems for considerable periods has been confirmed. His observations were not due to artifacts, as suggested by others. His interpretation, that the uptake was in response to a loss of water from the leaves, termed ‘subaqueous transpiration’, caused by metabolic activity of the mesophyll cells, was not supported by experiments with shoots of the same genus he used. The possibility that minute amounts of water can be actively excreted by shoots cannot be eliminated, but none could be detected under paraffin by microscopy. A more satisfactory explanation is that uptake was due to incorporation of water into cells during growth whilst ‘fully turgid’. This postulated growth uptake seems sufficiently large to explain all experimental observations to date and active water secretion need not be presumed.