The Problem of Impoverished Lands. 121 



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

 cabbage when it is pulled up ? 



Because the root-liairs and rootlets are so niimerons and in snch 

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

 extensive this contact is. 



6. What do you xinderstand hy a solution f 

 A substance dissolved in a liquid. 



Y. Give an example of a substance which will dissolve in water, 

 and one which will not. 



Sugar will dissolve ; sand will not. 



8. May materials which are insoluble in rain water be soluble in 

 soil water? Why? {Considt Less. 3.) 



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

 and this increases the dissolvino- power of water. 



9. Does warming the %oater increase its power to make substances 

 soluhle f 



Yes. 



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

 school book on physics or natural p)hilosophy.) 



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

 through a membrane or porous wall which separates them. 



11. Why does tJie soil water go into the root-hair f 



It is largely 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, tig. 3.) 



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

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



in the soil ; that is, it contains a lai-ger 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 woidd hap)pen if the liquid in the root-hair and that 

 in the surrounding soil were of equal density f 



There would be little or no movement of the water from the soil 

 into the root-hairs and the plants wovdd die. 



