36 ELEMENTS OF BOTANY. 
The rise of liquid in the tube is evidently due to water making its way 
through the thin membrane which lines the egg-shell, although this mem- 
brane contains no pores visible even under the microscope. 
53. Experiment 16. Osmose in a Begonia 
Leaf. — Place a little powdered sugar on the upper 
surface of a thick begonia leaf under a small bell 
glass. Watch for several days to see whether mois- 
ture from the inside of the leaf affects‘the sugar. 
The upper surface of this leaf contains no pores, even 
of microscopic size. 
54. Inequality of Osmotic Exchange. — The 
nature of the two liquids separated by any 
given membrane determines in which direc- 
tion the greater flow shall take place. 
If one of the liquids is pure water and the 
other is water containing solid substances 
dissolved in it, the greater flow of liquid will 
be away from the pure water into the solu- 
tion, and the stronger or denser the latter, 
Fig. 21.— Egg on the more unequal will be the flow. This 
Beaker of Water, : : 5 - 
to show Osmose, Principle is well illustrated by the egg-osmose 
experiment. Another important principle 
is that substances which readily crystallize, like salt or sugar, 
pass rapidly through membranes, while jelly-hke substances, 
like white of egg, can hardly pass through them at all. 
55. Osmose in Root-Hairs.— It is very easy to understand, 
from the principles just stated, that the soil-water (which is 
like ordinary spring or well water), separated by the delicate 
walls of the root-hairs and a thin lining of jelly-like liv- 
ing matter from the more or less sugary or mucilaginous sap 
inside them, will pass rapidly into the plant, while very little 
of the sap will come out. Probably most of the selective 
action, which causes the flow of liquid through the root-hairs 
to be almost wholly inward, is due mainly to the living layer of 
proteid material known as protoplasm (Chapter XIII), which 
