Experts in plant water relations are challenged to explain why the standard expression
for the water potential of an intact, transpiring leaf omits one of the pressure components,
namely the tissue pressure of the living leaf cells. Two questions are posed: A) Is
there a reason for omitting this component? B) If not, what evidence exists that it
may be ignored? When this component contributes significantly, the water potential
cannot be interpreted in the accustomed way as measuring tension in the xylem sap.
Tissue pressure - water potential - xylem tension
