126 ELEMENTARY BOTANY 
Take an empty jar I, and another jar IL, in 
which germinating seeds have been kept tightly 
corked for twenty-four hours. Pour lime-water into each jar 
and shake up. : 
The lime-water does not change in I., but 
becomes milky in II. 
There is little or no carbon dioxide in I. and 
enough in II. to be tested, therefore carbon 
dioxide has been given out by the germinating seeds. 
Put some ger- 
minating seeds 
into a jar, and also a test-tube 
containing caustic potash. Cork 
the jar with an india-rubber 
cork, into which has been fitted 
. a bent tube with coloured liquid. 
- The pressure of air 
in the jar gets less, 
and the liquid gradually rises 
along the bent arm of the tube. 
= As caustic 
potash is known 
to absorb carbon dioxide, the 
pressure of air in the jar is 
Fic 143.—Apparatus to show being diminished by the amount 
THAT PLANTS TAKE IN of oxygen taken in by the seeds, 
OXYGEN. a 
and the liquid rises because the 
pressure inside the jar is less than the atmospheric pressure on 
the exposed surface of the liquid in the bent tube. 
This experiment is more satisfactory than Experiment I., for 
in this case the carbon dioxide being absorbed by the caustic 
potash, the only change going on in the air of. the jar is the 
withdrawal of oxygen. These experiments show clearly that 
plants take in oxygen from the air and give out carbon dioxide. 
Take some germinating barley seeds and 
also some barley seeds which have been killed 
by boiling. Place them respectively in two vessels surrounding 
Experiment II. 
Result. 
Conclusion. 
Experiment III. 
Result. 
Conclusion. 

Experiment IV. 
