158 
HOW A PLANT -BREATHES 
ERHAPS you have heard people say that it is not 
good to sleep in a room with plants. 
They say this, because they have heard that at night 
the plant does not give out oxygen, but that it does 
give out the poisonous carbonic-acid gas. 
Now, you children know that part of this statement 
is’ true: 
You know that the plant cannot give out oxygen at 
night, because at that time there is no Sunbeam about 
to help Leaf Green tear apart carbonic-acid gas and 
send the oxygen back into the air. 
But how about the other part of the Atom 
Is it true that at night plants give out the poisonous 
carbonic-acid gas? 
Both day and night, plants give out carbonic-acid gas ; 
for though plants, save in the sunlight, cannot eat by 
means of their little green cells, they can breathe 
through the tiny mouths (Fig. 137) on the under side 
of the leaf by night as well as by day. 
And when either a plant or an animal breathes, it 
takes the life-giving oxygen from out the air mixture, 
and keeps it for its own use. But poisonous carbonic- 
acid gas is sent back into the air. Now, the question is, 
whether a plant does most good or most harm to the air 
by taking in and sending out the different gases. 
Of course, it does good when it lets the oxygen out 
through its cell walls, and stores away the carbon within 
itself; and it may seem to do harm when through its 
