Use of the Pressure Bomb for Hydraulic Conductance Studies

Stem sections of alfalfa (Medicago sativa L.) were subjected to forced flows of both water and high molecular weight dextran solutions. In either case, stems responded in accordance with the Ohm's law analogy for flow, i.e., flow was a linear function of pressure, at pressures ranging from 7.0–500 kPa and vacuum from 25.69 kPa. Since conductance values were the same for both pressure and vacuum powered flows, it is possible to extrapolate conductance values determined with a pressure bomb to negative pressure gradients experienced by plants.