186 TEXTBOOK OF BOTANY 



The major transformations of chemically bound energy among living 

 organisms may be summarized diagrammatically. 



Released by respiration in 

 green plants, animals, non- 

 Radiant energy j Chemically bound ^^ \ green plants; and by fire 



[ green plants ^--^^^ [ Retained in unoxidized plant 



and animal residues, such as 

 humus in soil, peat and coal, 

 petroleum, natural gas 



All animals eat large quantities of food in proportion to their gain in 

 weight. Evidently much more food is used in the animal body as a 

 source of energy than as a source of body material. Every time one 

 animal eats another it secures usually less than 10 per cent of the energy 

 the first animal obtained directly from plants. If a third animal eats the 

 second one, it derives less than 1 per cent of the energy in the plants 

 eaten by the first one. The animal population of a region cannot exceed 

 the supply of the chemically bound energy in the plants of that region 

 except in those instances v^here man is able to secure food from a foreign 

 market. 



Through such procedures as plant breeding, conservation of the soil 

 and water, the use of fertilizers, and improved methods of forestry, the 

 annual accumulation of chemically bound energy in plants may be 

 greatly increased, perhaps doubled or even more. But these procedures 

 require intelligent effort and foresight, and the elimination of wasteful 

 exploitation of natural resources. 



Summary. In the world of living organisms green plants have a unique 

 position. Except for their dependence upon certain groups of bacteria,^ 

 and the relatively few plants requiring cross-pollination by animals, they 

 are independent of other organisms. From one point of view all animals 

 are parasites upon the plant kingdom. Animals are not essential to 

 plant life. But animals and non-green plants are dependent upon the 

 green plants for chemically bound energy and certain synthesized prod- 

 ucts. Man in particular is dependent upon green plants for sugar, amino 

 acids, vitamins, precursors of vitamins, and, up to the present, for more 

 than 90 per cent of the energy he utilizes. In addition, there are thou- 

 sands of uses made of plants and plant products for convenience, recrea- 

 tion, and art. We are passing through a stage of development in this 



^ The importance of certain bacteria to green plants will become evident in the chapters 

 on non-green plants. 



