Eisco Ganong's Potometer

A potometer is an apparatus used to measure the rate of water loss, or transpiration, from a plant. In the Ganong's potometer, the rate of transpiration is determined by measuring the position of an air bubble in a graduated tube over a period of time. The change in position is caused by the plant absorbing water to replace an equal volume of water lost by transpiration.A plant shoot is sealed into a stopper which fits the end tube and the whole apparatus is filled with water, the open end of the capillary tube, which is graduated in millimetres, dipping into a beaker of water. The position of the air bubble may easily be adjusted by opening the glass stopcock to admit water from the reservoir.The apparatus is mounted on a wooden base with the tubes held by clips.