

78 THE WORK OF PLANTS 
Movement of water through membranes. This experi- 
ment illustrates the well-known behaviour of water 
and solutions of different kinds when 
separated by a membrane. Water moves 
quite readily through the membrane, but 
the substance in solu- 


' tion moves through 
with difficulty. Also 
the water will move 
Fic. 107. Puncturing 
a make-believe cell 
after it has been 
Sa Reina more readily in the 
direction of the 
stronger solution. ‘he fresh water has no substance, 
or but little, im solution. The sugar solution is stronger 
than the water, so the water moves readily through the 
membrane into it. 
Now when the vial containing the sugar solution is 
immersed in fresh water, some of the water flows 
through the mem- Ba al 3 
gs F 
brane into the sugar |” oe 
solution, because this Fre. 108. same as Fig. 107, Pca 7 


f é after needle is removed. 
is stronger. This 
increases the bulk of the sugar solution 
and it presses against the membrane, 
making it tight and firm, or rigid. 
When it is placed in the stronger solution, this draws 
some of the water out, and the membrane, losing its 
firmness, becomes flat again. 
