HOW THE LIVING PLANT UsHS WATER 77 
Now sink the vial in a very strong sugar solution 
for several hours. There should be go much sugar in 
the water that all of it will not dissolve. The mem- 
brane has become straight across again because the 
inside pressure is removed. Now sink it in fresh water 
again. ‘lhe inside pressure returns, and the membrane: 

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Fic. 106. Make-believe cell, at left before placing in water, middle one after lying in 
water has inside pressure, one at right after lying in very strong sugar solution 
has collapsed or become flabby. 
bulges again. Thrust a sharp needle through the mem- 
brane when it is arched or bulged, and quickly pull it 
out again. The liquid spurts out because of the inside 
pressure. , 
What is it that causes the inside pressure? Why is 
the inside pressure removed when the vial is immersed 
in the stronger solution ? 
