128 THE WORK OF PLANTS 
that this white substance is formed by the union of 
carbon dioxid and baryta-water. Pour some of the 
baryta-water down the sides of the jar and on the peas. 
Notice the white substance which is formed. 
Carbon dioxid from our breath. ‘l'ake some of the fresh 
lime-water or baryta-water and breathe upon it. This 
same white precipitate is formed, because there is 
a quantity of the carbon dioxid exhaled from our lungs 
as we breathe. It is interesting to show this close 
agreement between plant life and animal life. 
Plants take in oxygen gas while they breathe. Plants 
require oxygen in the process of respiration just as 
animals do. So far as the movement of the gases is 
concerned, respiration consists in the taking in of 
oxygen gas into the plant or animal body, and the 
giving off of carbon dioxid. 
To show that oxygen from the air is used up while 
plants breathe. Soak some wheat for twenty-four hours 
in water. Remove it from the water: and place it in 
the folds of damp cloth or paper in a moist vessel. 
Let it remain until it begins to germinate. Fill the 
bulb of a thistle tube with the germinating wheat. By 
the aid of a stand and clamp, support the tube upright, 
a lump of lime twice the size of a hen’s egg and put it in a quart 
of water. Allow it to settle and in a day or two pour off the clear 
liquid ; cork in a bottle before using. The white substance formed 
when lime-water is used is due to the union of the lime-water and the 
carbon dioxid. 
