IMBIBITION 147 



PROBLEM IV. HOW DO ROOT HAIRS TAKE IN WATER 

 AND SOIL SALTS? 



Demonstration 5. To show diffusion in gases and liquids. 



(a) Open a bottle of carbon bisulphide at one point in the school 

 room. Show, by raising of hands, the time it takes for the odor of 

 the gas to become noticeable in different parts of the room. (6) Place 

 a little powdered eosin in a glass of water. Leave undisturbed for some 

 hours. How long will it be before the entire glass of liquid is colored? 



Diffusion. We all know that certain substances, such as the 

 odor of tobacco smoke or the perfumes of flowers, pass rapidly 

 from the point where they are given off and tend to spread in all 

 directions through the air. The odor of the orange blossoms in 

 California is a memory to those who have driven near the orange 

 groves. Substances which will dissolve in liquids will also diffuse 

 through the liquids. In the diffusion of both gases and liquids 

 particles of the substance pass from the place where they are most 

 concentrated to where they are less concentrated, or lacking, the 

 rate of travel being much slower in liquids than in gases. 



Imbibition. The passage of water from point to point by 

 capillarity x does not account for soil water getting inside the cell. 

 It has to go through the cellulose wall and the delicate membrane 

 of protoplasm within. The walls of cells, like wood, absorb soil 

 water readily by a process known as imbibition (mi-be-bish'wn) 

 or absorption. This brings the soil water in contact with the cell 

 membrane. Inside the cell membrane is a liquid which would 

 diffuse freely with the soil water if the membrane were removed. 

 But a membrane acts peculiarly toward diffusing substances. 



Osmosis. The process by which water with dissolved substances 

 passes through the cell membrane is called osmosis. 



Demonstration 6. To show the process of osmosis. 



Carefully break away part of the shell of an egg so as to expose the 

 delicate skin or membrane underneath. Thus we have a picture of 

 the relation of the cell membrane (like the egg skin) to the cell wall 

 (like the egg shell). Suspend this egg in a glass of cold water half an 

 hour. What happens? 



If we test the water in the glass for protein, the organic sub- 

 stance of which white of egg is composed, we shall find none. 



1 Capillarity (kap-i-lar'i-ti) : rise of liquids in a tube. 



