49 BOTANY 
a few barley grains. Have in three separate tumblers, 
or better still, gas jars, as shown in the figure, water, 
a solution of caustic soda, and a solution of pyrogallie 
acid in caustic soda respectively. 
Now place the tubes with their clear ends dipping 
into the liquids, one in each jar. Then, with rubber 
corks, stop the ends containing the barley grains. The 
pyrogallic acid solution takes from the air in the tube 
the oxygen it contains, and, as about a fifth of the air 
_is oxygen, the liquid, to fill the place of the gas, rises 
in the tube to oceupy one-fifth of the space between 
the surface of the water and the cork. In this tube no 
germination will take place, no matter how long it may 
be left. It is to be noted that the oxygen is more 
readily absorbed if the inside of the tube is made wet 
with the solution at the clear end for about one-fifth 
of its length. 
In the tube dipping into water germination proceeds 
to a certain extent, indeed, till the enclosed oxygen is 
exhausted. Though the oxygen is used, the water does 
not rise in the tube. This, as we shall discover later, 
is due to the fact that the oxygen is replaced by exactly 
the same volume of carbon dioxide. 
In the tube dipping into caustic soda, germination 
proceeds to the same extent as in that dipping into 
water, but, since caustic soda absorbs carbon dioxide, 
the liquid gradually rises in the tube, till, by the time 
all the oxygen has been used and replaced by carbon 
dioxide, the space occupied by the liquid is again one- 
fifth of the tube. 
Light is not necessary to germination, as might be 
supposed from the fact that seeds germinate when 
buried in the ground, provided they are not too deep 
to receive a sufficient supply of oxygen. Indeed, 
seedlings in their early stages, develop more rapidly 
in the dark than in the light. Experiments to show 
this are easily devised. 
