Question

Suppose you have a small rose plant growing in a pot. How would you demonstrate transpiration in it?

Answer 1

Set-up A. Take a small well-watered potted plant, preferably one with broad leaves. Enclose the pot completely within a polythene bag and tie the mouth of the bag firmly around the base of the stem. This would prevent the escape of water vapour from the pot. Now cover the entire plant under a bell jar as in (A).
Set-up B. Arrange another similar plant and cover it with a bell jar exactly in the same manner as the first one, except that here you also keep a piece of dry cobalt chloride paper by the side of the plant inside the bell jar (B). The paper may be pinned to a wooden stick or to a strip of cork sheet.
Set-up C. Take a third bell jar without the plant, but still containing a similar piece of cobalt chloride paper (C). Now, keep all the three bell jars together in the sun.
After about half an hour we observe that,
1. The first bell jar (A) would show water vapour condensing on its inner walls.
2. The second bell jar (B) would also show a similar condensation and at the same time, the initially blue cobalt chloride paper in it would turn pink.
3. The blue colour of the cobalt chloride paper in the third bell jar (C) does not change at all and there are no water drops on the jar’s inner walls either.
The third bell jar in this experiment is a control which proves that there was no moisture in the air due to transpiration as there was no plant in it.