A A potted Ficus benjamina was placed on insulating foam inside a Faraday cage. Identical Platinum electrodes where inserted into the xylem (phloem removed) and a Petri dish containing a standardized water content soil solution of variable pH. The electrodes were connected to a high-impedance voltmeter. The standardized soil was connected to the pot soil via a 1 M KCl agar salt bridge (to complete the circuit via the soil-root interface). B Voltage vs Time post-electrode insertion shows no dependence on height, orientation or sap flow (it was stopped by inserting razor blades above and below the electrode) once transient voltages and currents are allowed to dissipate. The difference in pH between the xylem and the soil in this case is ~2. C The “streaming potential” voltage generation mechanism depends on the Zeta potential (ζ) -voltage difference due to different flow properties at the center of a capillary and its walls and the ΔP (pressure difference between the two ends of the capillary and is given by which, for typical values for a tree, yields between 1 and 10 mV. V_sapstream is such that faster flow leads to higher voltages.