76 SOIL AND ITS RELATION TO ROOTS 



part of it so carefully as not to tear the membrane directly under 

 the shell, then break the other end, insert a glass tube in it, 

 and cement the tube in place with sealing wax. Then place the 

 egg with the exposed membrane in water. 



Observations. — Are there any changes in the level of the 

 liquid in the tube? 



NOTE. — The process by which two fluids or gases, separated by a membrane, 

 pass through the membrane and mingle is called osmosis. The greater flow is usu- 

 ally from the less dense toward the denser medium. 



Test the water in the jar (if you used glucose in your artificial 

 cell) to see if glucose passed through the membrane. 



Conclusion. — 1. Explain, using one of the above experiments 

 as a basis, how osmosis takes place. 



2. How do root hairs take in soil water? 



3. What might help force liquids up the stem of the plant? 



Problem 57 : To determine what hind of substances will pass 

 through a membrane. 



Materials. — Glass jar, two thistle tubes, membrane or parch- 

 ment paper, starch, grape sugar, iodine, Fehling's solution, test 

 tubes. 



Method. — Fill two thistle tubes, one with glucose and water, 

 the other with starch and water ; tie membranes tightly over each. 

 Wash carefully to remove all starch or sugar from outside of tubes. 

 Then place each in a jar half filled with water. After 24 hours, 

 test contents of the jars, one for starch and the other for grape 

 sugar. (See lower figure, page 100, Civic Biology.) 



Observations. — Notice if any change has taken place inside 

 the thistle tubes. What changes take place after testing the 

 contents of the jar? 



Conclusion. — 1. Does starch or sugar pass through a mem- 

 brane by osmosis ? 



2. Can you make a generalization to cover soluble and insolu- 

 ble substances? 



NOTE. — Osmosis or exchange of gases will also take place through a membrane. 

 If carbon dioxide and oxygen gases were separated by a membrane, they would 

 tend to pass through the membrane and mingle with each other. 



