Determination rate of Transpiration using Ganong’s Potometer


  • A few drops of eosin oil is added to water to make it colored.
  • A freshly cut twig is placed on the mouth of the glass cylinder.
  • A single air bubble has to be kept at the zero reading of the horizontal bar. Lifting the bent end allows the air bubbles to enter and get trapped in the horizontal bar.
  • When the experiment begins, it is observed that the air bubble at the zero reading starts to move.
  • As the transpiration takes place, a transpirational pull is created by the shoot to make up for the loss. Due to this, the horizontal bubble starts moving in the direction of the twig. The transpiration rate is calculated by taking the distance covered by the air bubble in a certain time period. Several readings were noted by repeatedly adjusting the air bubble to zero. The average of these readings gives the transpiration rate.