Experiment to demonstration transpiration in a young shoot...
Aim:- To show that a potted plant loses water vapour from its leaves.
Method:- A rubber sheet is used to cover the pot and part of the stem of the potted plant. This prevents water evaporating from the soil and the stem. The potted plant is placed on a vaselined glass plate. The potted plant is then covered witg a dried bell jar 'A' and placed on a sunny place. The control experiment B is set in the same manner but with the leaves of the potted plant removed.
Result:- After twi hours, drops of colorless liquid collect on the inside of the bell jar A. No such drops of colorless liquid collect on the inside of the bell jar B.
Conclusion:- Since the pot and soil are covered, the presence of water in the experiment shows that plant loses water through the leaves. Since the bell jar was not in contact with leaves, the loss of water is by vapour.
Precaution:- It us important to invert the bell-jar over a flat vaselined glass-sheet on which the potted plant is placed. This is to prevent the leakage of air into and out of the bell-jar into the atmosphere. Air contains some amount of water vapour which can also leak into the apparatus if unprevented.