QUESTIONS AND SUGGESTIONS 121 



C. 9. Describe fertilizers and their use. 10. What are the various 

 ways in which they may affect fertility ? n. The fertility of soil de- 

 pends a good deal upon its ability to hold moisture ; i.e., other things 

 being equal, soil which remains moist (if not too moist) will be more fer- 

 tile than that which dries out quickly. Why is this so ? Devise an 

 experiment for testing samples of soil in order to determine their 

 relative capacity for retaining moisture. 12. How does the farmer 

 increase the capacity of his soil to retain moisture ? 13. Devise an 

 experiment to demonstrate how, by different treatments, the capacity 

 of soil to retain moisture may be increased. 



Section 35. 1. Describe the structure of a root-hair and the 

 conditions which surround it. What is its chief function ? 2. What 

 is cellulose ? 3. What is osmosis ? 4. Describe a method of demon- 

 strating osmosis. 5. Explain what is meant by osmotic pressure. 



Section 36. 1. Define transpiration and the transpiration stream. 

 2. What is the principal cause of the continuous entrance of water 

 into the plant? 3. What are the principal causes of the continuous 

 entrance of solutes into the plant? 4. What is it that transforms 

 the solutes which enter the plant ? 5. Why do some solutes pass 

 out of the plant into the soil ? 6. Why is it that animals are not so 

 dependent upon osmotic movements as plants are ? 7. What are 

 the two kinds of movements which occur within the plant body? 

 8. Give the description of the movement of solutes which is quoted 

 in the text, and explain what is meant by high and low osmotic 

 pressures. 9. How much of the weight of common plants is water ? 

 Why do they need so much water ? 10. What are some plants which 

 grow well in dry places ? n. What crops are most injured by drought ? 

 12. What crops are least injured by drought? 13. What crops do 

 well on sandy soil? 14. What plants do you know which grow in 

 the water? 



Section 37. 1. Define energy and give examples of it. 2. Define 

 latent energy and give examples of it. 3. Give examples of various 

 "forms of energy," and of the transformation of one form into another. 



4. What are some of the principal practical uses which man makes of 

 the fact that one form of energy can be transformed into other forms ? 



5. Describe ''nature's invention" for storing up the energy of light. 



6. Describe the formation of coal. 7. Does it seem possible for ani- 

 mals to have existed before plants ? Explain your answer. 



