—_—— 

130 | THE WORK OF PLANTS 
germinating. From our study of germinating peas we 
know that a suffocating gas, carbon dioxid, is given off 
while they breathe. The caustic potash solution or the 
baryta-water, whichever is used, absorbs the carbon 
dioxid. The carbon dioxid is heavier than air, and so 
settles down in the tube, where it can 
be absorbed. 
Where does the carbon dioxid come 
from? We know it comes from the 
breathing, growing seedlings. You 
will remember that the symbol for 
carbon dioxid is CO, The carbon 
comes from the plant, because there 
is not enough in the air. The nitro- 
gen of the air could not join with the 
carbon to make CO,; so it must be 
that some of the oxygen of the air 
joins with the carbon of the plant. 
a. Yes, it does; but the oxygen 42am 
absorbed by the plant. When it gets into the living 
plant substance, some of the carbon breaks away from 
its association with the living substance and hurries to 
join the oxygen, and together they escape into the alr. 
When plants breathe fast they are doing more work. 
From what we have just learned we see that some of 
the living plant substance is used up or consumed 
while the plant breathes. When a fire burns, oxyge? 

