bows 
HOW PLANTS BREATHE 129 
as shown in Fig. 158. Let the small end of the tube 
rest in a strong solution of caustic potash (one stick 
caustic potash in two-thirds tumbler of water) to which 
red ink has been added to give a deep red colour. Place 
a small glass plate over the rim of the bulb and seal 
it air-tight with an abundance 
of vaseline. Two tubes can be 
set up in one vessel, or a second 
one can be set up in strong 
baryta-water coloured in the 
same way. 
The result. You will see that 
the solution of caustic potash 
rises slowly in the tube. The 
baryta-water will also, if that 
isused. The solution is coloured 
so that you can plainly see it 

rise in the tube, even if you are 
] 1 ; ers. h 
a6 4 little distance from it.. In: = Sa 
‘“‘ breathing’ of germinating 
the experiment the solution in yee 
six hours had risen to the height shown in Fig. 158. 
In twenty-four hours it had risen to the height shown 
in Fig. 159. | 
Why the solution of caustic potash rises in the tube. 
Since no air can get into the thistle tube from above 
or below, it must be that some part of the air which 
is inside the tube is used up while the wheat is 
