Question

What is a potometer?

Answer 1

Potometer is a device that measures the rate of water intake by a plant (L. poton: drink, meter: measure), and this water intake is almost equal to the water lost through transpiration.
A twig of some suitable plant cut with a sharp knife is fixed in an apparatus as shown in fig. The entire apparatus is filled with water so that no air spaces are present. An air bubble is introduced into the horizontal graduated capillary tube while dipping into the beaker containing water.[This is done by lifting the bent capillary tube in the coloured water so that air may be sucked in due to suction pull and is again dipped into the water.] As transpiration proceeds, i.e., as the water is lost from the twig, a suction force is set up which pulls the water from the beaker and the bubble in the capillary tube moves along. The readings on the capillary tube moves along. The readings on the capillary tube would give the volume of water lost in a given time. The air bubble can be brought back to its original position by releasing some more water from the reservoir into the capillary tube by opening the stop cock.