Record your findings. Draw conclusions concerning the specific conditions which 

 favor the growth of plants in the distinct habitats which you visit. 



5 To contrast the topsoil in a forest and in a run-dovn cultivated field, select 

 two locations similar in all other respects, and examine the soils. With a spade dig a 

 hole through the topsoils in each case. Determine how they compare in depth, in 

 proportion of organic material to sand and clay, in water-absorbing and water- 

 holding capacity, in amount of decay that is taking place, in compactness, in resist- 

 ance to erosion, and in other features. Record your findings. Relate what you have 

 found with reference to the effect of forests upon fertility and upon floods. 



QUESTIONS 



1 What kinds of living things can be entirely independent of other organisms.? 



2 Why cannot all hving things be entirely independent of others.'' 



3 Why are there more parasites among microbes than there are among the 

 larger plants and animals.? 



4 Why is it important to distinguish between symptoms and causes of diseases.? 

 Why is it important to know the symptoms and the causes of diseases.? 



5 How can the abundance of a particular species of plant or animal (reindeer, 

 oranges, whales, cotton, sugar cane, sheep, cattle) influence the whole mode of life 

 of a community? 



6 How may certain physical features act as barriers to the spread of some 

 species, and at the same time aid in the distribution of others.? 



7 In what ways are conditions in a pioneer community like those in a climax 

 community.? In what ways diff^erent.? 



8 What factors bring about the normal shift within a community toward the 

 climax grouping of organisms.? 



9 What are some of the advantages of carrying the division of labor still 

 farther among individuals.? among nations? What are the disadvantages.? 



10 Is a person with a special talent better off in a large community or in a small 

 one.? Why.? How about a person with a special handicap? 



11 In what respects are human communities Hke those found in nature.? In 

 what respects different.? 



577 



