Materials released from organisms, living and dead, pass on into others, 

 each particle in the course of years having been part of many organisms. 



Where a balance has been established through the interaction of many 

 different plant and animal species, intruding man often disturbs existing rela- 

 tionships by destroying what he would like to preserve or by increasing forms 

 that he considers objectionable. 



EXPLORATIONS AND PROJECTS 



1 To investigate certain advantages and disadvantages of specialization, com- 

 pare the relative effectiveness with which different species of plants and animals 

 carry on particular functions. For example, we might compare earthworms with 

 caterpillars and with adult insects as to the speed and effectiveness of locomotion, 

 the manner of food-getting, and recovery or regeneration after injury. Compare 

 structures and living habits of various parasites of birds and mammals and of the 

 dodder, a common parasite of clover. Relate the characteristic stages and special- 

 ized structures to the mode of life. Show wherein specialization is an advantage; a 

 disadvantage. 



2 To investigate the physical conditions involved in certain plant associations, 

 visit a neighboring woodland and compare the growth on different slopes, on differ- 

 ent soils, and under different moisture conditions. Note the relative heights of the 

 trees, the kinds of trees growing, the density of the shade, the number of species, the 

 luxuriance of the growth, the dominant forms, the presence of simple pioneer plants, 

 and any differences in the kinds of animal life found in the various plant associations. 

 Summarize the results of observations by relating the various physical conditions to 

 the kinds of plant associations found. 



3 To find the relation of crowding upon growth, plant seeds of a rapidly growing 

 plant very close together in one pot, and widely separated in a second pot. Maintain 

 optimal growth conditions in both pots for several weeks and compare results. 

 Account for differences in terms of physical conditions that limit development. 



4 To investigate the problems associated with a shifting population, find out 

 how the population of the United States is distributed and how this population has 

 shifted during the past seventy or eighty years; relate these shifts to conditions 

 that brought them about and to their effects upon economic resources and develop- 

 ments.^ Construct a large map showing present centers of population; list the chief 

 areas in which population is centered; indicate on the map or on the lists or on both 

 the chief contributions to human life in each area. 



5 Report on population shifts resulting from the development of a new 

 industry, from the discovery of mineral resources, from changes in the soil or in 

 the water supply, from the emergency needs of the Second World War, or from 

 the introduction of better means of transportation, as railroads, highways, or air 

 fields. 



^Refer for information to the National Resources Committee report The Problems of a Changing 

 Population, May, 1938, or to an atlas or to a geography. 



538 



