182 TEXTBOOK OF BOTANY 



the algae. Without this compensation the fish would soon starve to death. 

 It is assumed that the reader can account for all six of the conditions 

 listed above. Perhaps vitamins should also be considered. 



Since an adequate supply of inorganic salts was included in the soil, 

 they may be ignored in this discussion. The presence of bacteria that 

 cause decay undoubtedly prolongs the duration of the microcosm. They 

 may digest and oxidize cell structures that are not acted upon by the 

 enzymes of the fish and algae, and by this means delay the time at 

 which the supply of carbon dioxide in the bottle becomes inadequate. 



Perhaps it is evident that the algae and certain decay-producing bac- 

 teria could exist together in this bottle without any animal being present. 

 The animals are dependent upon the plants, but the plants are not de- 

 pendent upon the animals. They were placed in the bottle merely to 

 imitate natural conditions. Even if all the animals in nature were de- 

 stroyed, most of the plants would still survive indefinitely. Only those 

 that are dependent upon the cross-pollination effected by animals, and 

 those that are strictly parasitic upon animals would perish. 



A human cosmos. Our second case, man in the United States, is some- 

 what more complicated because man uses plant products and the 

 chemically bound energy of plants in many ways in which the fish does 

 not. Food is used in the body of man in the same manner in which it is 

 used in the body of a fish: as a source of chemically bound energy, and 

 as a source of material that is transformed into the substances of which 

 cells are composed. Moreover, food is used in this same manner in the 

 bodies of the many domesticated animals which man employs in various 

 ways. The dependence of man and his domesticated animals upon green 

 plants for sugar, amino acids, vitamins, and a supply of chemically bound 

 energy necessary to body processes probably does not need further 

 emphasis. 



Many of the uses which man makes of the material products of plants 

 are also familiar to all of us. That plants are the main source of all the 

 energy employed by man is not so well appreciated. The remainder of 

 this chapter, therefore, will be devoted primarily to his dependence upon 

 plants as a source of energy. 



In addition to the energy that is transformed in the bodily processes 

 of man and his domesticated animals, man employs energy as heat, light, 

 electricity, and mechanical power in his home, in public buildings, on 

 the street, on the farm, in the factory, and on the highways. Less than 

 10 per cent of all this energy is obtained from wind and water power. 



