Using a system developed in France, relative sap flux was measured in trunks and frinds of palms in relation to the potential evapotranspiration (PET) and evapotranspiration (ET) rates deduced from micrometeorological measurements. The method provided a sensitive means of detecting changes in transpirational activity related to radiation, PET, soil water supply and frond aging. Its further use and development are discussed.

Keywords: evapotranspiration, plant water relations, sap, soil water