30 NEW ZEALAND NATURE-STUDY BOOK 
solutions in sufficient quantity to furnish the necessary 
supplies of food. , 
Then again, transpiration helps to draw the water 
containing the dissolved plant food up the stem, and 
tends to make the roots absorb liquids more quickly. 
A simple experiment will illustrate this. Take a small 
thistle funnel and tie over the wider end, or mouth, a piece of 
dialysis paper. The paper should be 
soaked in water for some time pre- 
viously and must be tightly tied over 
the funnel. Pour into the small end 
of the funnel some syrup or brine, 
and dip the large end into a basin 
of clear water. Ina short time it 
will be seen that the liquid is rising 
in the tube. On tasting the water 
in the vessel it will be found that 
some of the sugar or salt has come 
- through the membrane, ‘This 
property of liquids separated by a 
membrane to pass into each other 
is: known as diffusion. It will be - 
noticed that both liquids have 
diffused through the membrane; but 
that the thinner liquid has diffused 
more rapidly than the thicker one. A plant is wholly made 
up of little cells or chambers, separated from each other by 
thin walls through which liquids are able to pass. The 
liquid in the small root hairs is denser than the water 
outside, and so the latter diffuses into the former, and with 
it the plant food held in solution. The water which enters 
these cells is less dense than that contained in neighbouring 
cells, so that some of it passes up into these, and so 
on into cells higher and higher up the plant. As the 
Fig. 26. 
