128 : HEE MENTARY BOTANY 
The next experiment shows that carbon dioxide is given 
out by animals in breathing. | 
Take a vessel with lime-water and breathe into 
"it for some minutes. 
Result. The lime-water turns milky. 
Conclusion. = Carbon dioxide has been given out in breathing. 
As breathing involves the breaking down of 
protoplasm, there must be a building up of fresh 
protoplasm by the plant to repair the waste. ‘The first step 
in this process is assimilation. | 
Green plants obtain carbon dioxide from the air. It is 
not easy to show this directly, 
because carbon dioxide is con- 
stantly being given out in 
respiration. It can, however, 
be shown experimentally that 
under certain conditions green 
plants make starch out of 
carbon didxide taken from the 
air, and water obtained from 
the soil. It is therefore as- 
sumed in the following experl- 
ments that the presence of 
starch shows that the plant has 
been taking in carbon dioxide 
from the air. The test for starch 
Fic. 145.—Appararus to show 18 lodine, which turns it blue. 
Experiment VI. 
Assimilation. 

THAT PLANTS WILL NOT MAKE Take two pots 
STARCH WHEN DEPRIVED OF Experiment A. 
CARBON DIOXIDE. of Clover, A and 
B. Cover each with a bell-jar. 
A has a U-tube containing soda-lime passing through the 
stopper of the bell-jar. Soda-lime absorbs carbon dioxide, so 
that the air which reaches the Clover is freed of carbon 
dioxide. Some caustic potash should be placed under the 
bell-jar of A to absorb the carbon dioxide breathed out by the 
plant. Pot B has attached to it a U-tube open to the air. 
Expose both pots to the sun for some time—an hour or 
