To find out the relation between transpiration and absorption.
A bottle with a graduated side-tube and a split rubber cork are required for this experiment. A small rooted plant is introduced through the split cork into the bottle which is filled with water. The level of water is noted in the side-tube, and a few drops of oil poured in here to prevent evaporation of water from the exposed surface. The connexions are, made air-tight. The whole apparatus is then weighed on a balance, and the weight noted.
After a time it is observed that the water-level has fallen, indicating the volume of water that has already been absorbed by the plant. The apparatus is then re-weighed and the difference in weight evidently shows the amount of water that has transpired from the leaf-surface. If the experiment is continued for a period of 24 hours it will be seen that the volume of water in c.c. absorbed is slightly greater than the amount of water in grams lost by transpiration.
Thus the relation between transpiration and absorption can be worked out for the various hours of the day and under diverse external conditions. This experiment not only shows the relation between the two processes, transpiration and absorption, but also separately proves absorption and loss of water by transpiration.