The Problem of Impoverished Lands. 121 



5. Why do particles of soil adhere to a young plant of wheat or 

 cabbage ichen it is pulled itpj f 



Because the root-hairs and rootlets are so luimerons and in such 

 close contact with the soil. The liner the soil, the closer and more 

 extensive this contact is. 



6. What do yo\i understand hy a sohition f 

 A snbstance dissolved in a liquid. 



7. Give an example of a substance which will dissolve in water ^ 

 and one vnhich will not. 



Sngar will dissolve ; sand will not. 



8. May ^materials which are insohible in rain water be soluhle in 

 soil water f Why? {Consult Less. 3.) 



Yes. Because the soil water contains carbonic acid gas in solution 

 and this increases the dissolvina^ power of water. 



9. Does wainning the loater increase its power to make substances 

 solidjle f 



Yes. 



10. Write a definition of osmosis. {Consult dictionary or some 

 school booh on physics or natural philosophy }j 



It is the tendency of two liquids of different density to pass 

 through a membrane or porous w^all which separates them. 



11. Why does the soil icater go into the root-hair? 



It is largel}^ on account of this osmotic tendency or action. The 

 outer walls of the little root-hairs constitute the membrane ; the sap 

 or moisture in the cells of the root-hairs and the soil-moisture 

 represent the two liquids separated by the membrane. (See Reading- 

 Lesson 4, lig. 3.) 



12. Why does not the liquid in the root-hair flow out into the soil ? 

 Because the sap in the hairs is denser than the water or moisture 



in the soil ; tliat is, it contains a larger percentage of solid matter in 

 solution. When two liquids of different density are separated by a 

 membrane, the passage of the liquid through the membrane is in 

 the direction from the less dense to the more dense. 



13. What luoidd happen if the liquid in the root-hair and that 

 in the surrounding soil were of equal density f 



There would be little or uo movement of the water from the soil 

 into the root-hairs and the plants would die. 



