THE MAINTENANCE OF THE INDIVIDUAL 



XIV 



THE ROLE OF GREEN PLANTS 



Preview. Structure of green plants • The raw food materials used by 

 plants • The root and its work • The stem, structure and function • The 

 structure of the leaf • How green plants make food ; carbon dioxide as raw 

 material ; the role of water ; chlorophyll and light ; relation of artificial 

 light to food making ; what goes on in the green leaf in sunlight ; chemistry 

 of food making • Enzymes and their work • How food is used by the plant 

 body • Respiration • Transpiration • The rise of water in plants • Produc- 

 tion of oxygen by plants • Suggested readings. 



PREVIEW 



It is a trite statement to say that the destiny of man on the earth 

 depends upon green plants. All living stuff is made up of the ele- 

 ments found in air, in water, and under the earth's surface, yet 

 no laboratory technician has ever been able to put this material 

 together and make protoplasm. That energy is displayed by plants 

 and animals is obvious, but no man has ever been able to energize 

 matter and create a living organism. We know that the units of 

 structure, the cells, do release energy and that this energy comes, as 

 does all other energy, from the oxidation of fuel substances. Such 

 fuels used by living things we call foods. Moreover, these foods, 

 be they from plant or animal, in the long run depend upon energy 

 derived from the sun. The Biblical declaration that ''all flesh is 

 grass" is literally true, for without green plants animals would have 

 no food. 



We do not think of plants as very dynamic objects compared with 

 animals. Nevertheless, if we look at the soil pushed up by growing 

 seeds, the pavement broken by the growth of trees, and even the 

 hardest rocks split apart by the wedge action of growing stems and 

 roots, we realize that plants are very much alive. They respond to 

 the various stimuli in the environment, reacting like animals to 

 temperature changes, to gravity, to various chemical substances, or 

 to the directive force of currents of water. 



Unlike animals, whose metabolism is catabolic, the green plant's 

 metabolism is more completely anabolic. It builds up materials to 



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