QUESTIONS AND SUGGESTIONS 119 



vealed indicates the existence in living bodies of no laws 

 of matter different from those which operate in non-living 

 bodies, nor of any elementary substance different from the 

 elementary substances which exist in non-living bodies. 

 Seeming differences have disappeared as knowledge in- 

 creased. Just why certain conditions do cause certain 

 life changes we cannot say ; just why certain conditions, 

 for example, cause a seed to sprout we do not know; our 

 knowledge may never reach that point. But the changes 

 themselves, once started, operate under the same laws as 

 all other changes. The powers of living things are different 

 from the powers of non-living things, but all these powers 

 are subject to the same laws of matter. 



So plant life, as far as we understand it, is simply a 

 great complex of physical and chemical changes. Evi- 

 dently you can understand very little about plants with- 

 out understanding something of the nature of such changes 

 and of the laws under which they operate. 



QUESTIONS AND SUGGESTIONS 



Section 28. Make a list of questions whose answers would ex- 

 plain things recently mentioned in the book or in the class which 

 you do not understand. 



Section 29. 1. Describe what happens when one substance is 

 dissolved in another. 2. Make a list of the substances which you 

 know will dissolve in water. 3. What is the difference between 

 "soft" water and "hard" water ? 4. Why is soft water better than 

 hard water for washing ? 5. Why is it easier to wash in soapy water 

 than in clear water ? 6. Explain the relation of the temperature of 

 water to the rate at which substances dissolve in it. 7. Define solute 

 and solvent. 8. Why is it necessary to understand solution in order 

 to study the processes of life ? 9. Explain in what way the water 

 which comes from springs is different from the water which falls as 

 rain. 10. Explain why distilled water is pure water. 11. State the 



