Water relations of plants in the field: Some comments on the measurement of selected parameters

Methods for the analysis of water status and transport in the soil-plant-atmosphere continuum are briefly enumerated, with some personal comments on their reliability when used on plants growing in the field. These methods have provided us with a coherent system of data essentially free from major contradictions to the cohesion theory of water transport. It is shown that recent attempts at replacing the xylem tensions postulated by this theory with hypothetical osmotic transport mechanisms in order to accommodate data from the xylem pressure probe are not consistent with the bulk of results and furthermore are implausible in view of the energetic expenditure required.