CHAPTER I 





PLANT SCIENCE 



Every animal is in some way dependent upon plants every moment of 

 its life. One may well begin the studv of botany by inquiring into the 

 ways in which man and other animals of his own community are de- 

 pendent upon plants and plant products, or are otherwise influenced by 

 plants. This local survey may be extended into other communities and 

 geographic regions. If the inquiry is also projected into historic and pre- 

 historic records one may learn how plants and a knowledge of plants 

 have played a significant and at times a decisive role in the advance and 

 decline of civilizations in many parts of the world. 



Everywhere man and other animals use plants directly as food, or eat 

 other animals that feed on plants. Directly or indirectly all animals are 

 dependent upon plants as the source of food. During the growth of the 

 animal a part of this food is transformed by physiological processes into 

 the substances of which the body is composed. A larger part of it is 

 oxidized within the tissues of the animal, and energy is liberated. As a 

 result of this liberated energ\' the temperature of the bodv of the animal 

 is often maintained above that of its surroundings, and the animal is 

 also able to move about and to do other kinds of work. 



Through the burning of such plant derivatives as wood, coal, petro- 

 leum and gas in furnaces or engines man secures light, heat, electricity, 

 and mechanical energv by which he has been able to modify his immedi- 

 ate environment, supplement his own ability to move about, and trans- 

 port materials and supplies wherever they are needed or desired. These 

 two products of green plants — food substances and chemically bound 

 energy — are indispensable to all living organisms. 



There are also certain substances derived from plants which are essen- 

 tial to the health and well-being of all animals — for example, the vitamins 

 and mineral elements bound in organic compounds. 



With the progress of civilization many other plant products have be- 

 come indispensable or at least highly desirable. From plants we obtain 

 the materials of which most of our houses are built, finished, and fur- 



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