Abstract: | A thermocouple psychrometer method, previously described foruse in determining tissue and sap water potentials, has beenadapted for determining matric potentials. Matric values ranging from approximately zero to 10 x105 Pa were observed with wilting wheat leaves. Mean valuesof total tissue water potential and of its solute (osmotic),matric, and cell wall pressure components were 16.6,18.3, 30 and +4.7 Pa x 105, respectively. Matric potentials are often ignored in investigations of plantwater relations. This practice is shown to result in underestimationof wall pressures (in this case by a mean of 64 per cent) andsometimes in spuriously negative values. |