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potometeran instrument designed to measure the rate of absorption of water by a cut shoot and hence, indirectly, the rate of TRANSPIRATION by the shoot in a particular set of conditions, which can be varied.
At the start of the experiment an air bubble is introduced into the tubing adjacent to the graduated scale. Reservoir A supplies water to replace that lost by the shoot, the amount taken up being indicated by the movement of the air bubble along the scale. Opening the stopcock at the end of a time period causes water from reservoir B to force the air bubble along the tube, ready for a fresh start.