128 TEXTBOOK OF BOTANY 



ciples represented. Here again certain interrelations between two dif- 

 ferent environmental factors and the rate of photosynthesis are evident. 



Summary. The rate of photosynthesis is dependent upon the interrela- 

 tions of several external factors and certain conditions and processes 

 within the plant cells. Some of these factors affect photosynthesis di- 

 rectly, others less directlv through a series of other processes. The impor- 

 tant external factors that most directlv affect the rate of photosynthesis 

 are the intensity and kind of light, the concentration of carbon dioxide in 

 the air or water environment, the temperature, and water — though most 

 of the effects of water on photosvnthesis are indirect. Among the impor- 

 tant internal conditions are the amount and distribution of chlorophyll 

 and enzymes, and such structural features as stomates, intercellular 

 spaces, and veins, which influence the movement of materials into and 

 out of the chlorenchvma. 



The importance of photosynthesis to all living organisms will be appre- 

 ciated better as it becomes more evident, from the facts in later chapters, 

 that all the organic compounds in the bodies of plants and animals and 

 all the commercial products obtained from them have their beginning in 

 the synthesis of sugar. When it is clear that the chemically bound energy 

 supply of the bodies of all living organisms, and most of the energy that 

 we use in our homes and industries can be traced back to the radiant 

 energy chemically bound in sugar, we can view photosynthesis in true 

 perspective. 



REFERENCES 



Meyer, B. S., and D. B. Anderson. Plant Physiology. D. Yan Nostrand Com- 

 pany, Inc. 1939. 



Miller, E. C. Plant Phi/siology. 2nd ed. McGraw-Hill Book Company, Inc. 

 1938. 



Spoehr, H. A. Photosynthesis. Chemical Catalog Company, Inc. 1926. 



