For demonstration of transpiration rates and rates of water absorption by a cut shoot under various external conditions. Apparatus mounted on bakelite base with PTFE key stopcocks by clips. Potometer Ganong\’s with Glass stopcock on bakelite stand. Diameter of reservoir 20 mm, capillary bore 1 mm.

A potometer, also known as a transpyrometer, is a device used to measure the rate of water uptake by a leafy shoot, which is nearly equal to the water lost through transpiration. The causes of water uptake are photosynthesis and transpiration.

The rate of transpiration can be estimated in two ways:

1. Indirectly – by measuring the distance the water level in the graduated tube falls during a measured period. This is assumed to be due to the cessation of water intake, which must replace an equal amount of water lost by transpiration.
2. Directly – by measuring the decrease in mass of the potometer over a given period. Here it is assumed that any loss of mass is due to transpiration.