The apparatus shown in the following diagram is Garreau’s potometer designed to demonstrate unequal transpiration from the two surfaces of a dorsiventral leaf Before keeping the leaf in between the cups, anhydrous calcium chloride (CaCl2) contained in two small vials were weighed and placed in both the cups. The ends of the cups were closed with corks through which two mercury manometers were connected. After few hours, CaCl2 vials were taken out and weighed again.
What is the purpose of keeping CaCl2 vials inside the cup?
CaCl2 is a hygroscopic compound that absorbs moisture/water without changing its state. CaCl2 vials inside the cup to absorb water.