The apparatus shown here is Girreau’s poto-meter 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 a few hours, CaCl₂ vials were taken out and weighed again.

(i) What is the purpose of keeping CaCl₂ vials inside the cup?

(ii) After a few hours, the CaCl₂ vials were taken out and weighed again. Will you expect any difference in weight ? If so, give reasons.

(iii) What was the purpose of using a mano-meter?

(iv) What do you mean by transpiration?