HOW PLANTS GIVE OFF WATER Se UE 
accumulation of the moisture may often be hastened 
or increased at certain places on the jar by holding 
a piece of ice near the jar outside. The cold glass 
condenses the water vapour into water again, in the 
same way that the cold air above condenses the water 
vapour as it arises from the earth, first forming clouds 
and later raindrops. The living plant, then, loses water 
through its surface in the form of water vapour. 
A delicate test for the escape of water vapour from 
plants. A very pretty and delicate test for the escape 
of water vapour from living plants can be made in this 
way. Make a solution of a substance known as cobalt 
chloride in water. | 
Saturate several 
pieces of filter paper 
with it. Allow them 
to dry, and then dry 
them still more thor-— 
oughly by holding 
them near a lamp or 
gas jet, or In a warm 
oven. You will ob- 

serve that the water 
Ss olution of CO b alt Fia. 133, A good way to show that the water passes 
chlori de is re d. The off from the leaves in the form of water vapour. 
wet or moist paper is also red, but when tt 2s 
thoroughly dry it is blue. It is so sensitive to moisture 
