123 (0 ELEMENTARY 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. ee 
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 dioxide taken from the 
air, and water obtained from 
the. soil. It is therefore as- 
sumed in the following experi- 
ments that the presence of 
starch shows that the plant has 
been taking in carbon dioxide 
from the air. The test for 
Fic. 145._Appapatts To sHow . Starch is iodine, which turns it 
THAT PLANTS WILL NOT MAKE lye, 
STARCH WHEN DEPRIVED OF 
CARBON DIOXIDE. 
Experiment VI. 
Assimilation. 

Take two pots 
of Clover, A and 
B. Cover each with a bell-jar. A has a U-tube containing 
caustic potash passing through the stopper of the bell-jar. 
Caustic potash absorbs carbon dioxide, so that the air which 
reaches the Clover is freed of carbon dioxide. 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 
two. Take a leaf off each. Boil the leat in water for a 
Experiment A. 
