GANONG POTOMETER
Used to measure the rate of water absorption by a cut plant shoot, which closely relates to the rate of transpiration. It consists of a main glass tube, a graduated horizontal capillary tube, a water reservoir with a stopcock, and a wide-mouthed tube to hold a leafy plant twig.
Apparatus consists of a Boro 3.3 Glass apparatus comprising of horizontal graduated tube which is bent in opposite directions at the ends. One bent end is wide and the other is narrow. A reservoir is fixed to the horizontal tube near the wider end. The reservoir has a Glass stopcock to regulate water flow. The apparatus is filled with water from reservoir. A twig or a small plant is fixed to the wider arm through a split cock. The other bent end of horizontal tube is dipped into a beaker containing colored water. An air bubble is introduced into the graduated tube at the narrow end keep this apparatus in bright sunlight and observe. As transpiration takes place, the air bubble will move towards the twig. The loss is compensated by water absorption through the xylem portion of the twig. Thus, the rate of water absorption is equal to the rate of transpiration.