Chapter 5 

 The Chemistry of Photosynthesis 



From the chemical viewpoint the first definite observation of value 

 regarding the phenomenon of photosynthesis was made by Priestley in the 

 discovery that plants are capable of forming oxygen. This fact was 

 further elaborated by Ingen-Housz who showed that plants absorb carbon 

 dioxide and emit oxygen in the light and by Senebier that only those por- 

 tions of plants bearing chlorophyll have this capacity. It was realized 

 already at this time that in the dark the gaseous exchange of plants goes 

 in the opposite direction. Through the combined investigations of Ingen- 

 Housz and of Senebier the role which photosynthesis plays in the develop- 

 ment of plants and that of plants in the economy of all living organisms 

 was greatly advanced, lla^ed upon the newer conceptions of Lavoisier, de 

 Saussure established quantitative relations between the amounts of carbon 

 dioxide absorbed and of oxygen emitted in photosynthesis and demon- 

 strated the importance of water in the photosynthetic reactions. To these 

 facts were added the observations of von Mohl regarding the role of the 

 chloroplasts and about twenty years later those of Sachs relating to the 

 formation of starch as the first visible product of photosynthesis. At 

 about the same time Boussingault had expressed the idea that glucose was 

 the first product formed in the photosynthetic process. These were 

 roughly the facts with which the chemists in about the middle of the 

 nineteenth century were familiar. 



With the development of organic chemistry under Liebig. Dumas, 

 Laurent, Gerhardt. Woehler and others, it became possible to formulate 

 theories and chemical conceptions of the mechanism of the molecular re- 

 actions involved in the reduction of carbonic acid to carbohydrates. Some- 

 thing was known of the chemistry of the materials which enter the re- 

 action as well as of the products which are formed. It seemed possible 

 to subject the phenomenon of photosynthesis to the same method of reason- 

 ing which had been employed in interpreting other reactions of organic 



compounds. 



The literature on the chemistry of photosynthesis which has accumu- 

 lated during the past seventy-five years is quite voluminous. A careful 

 perusal of these writings clearly reveals certain facts concerning the man- 

 ner in which tlie problem of photosynthesis has been attacked as well as of 

 the nature of the problem itself. Considering the importance of the phe- 

 nomenon of photosynthesis, its great economic significance, the fact that 



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