THE THEORIES OF PHOTOSYNTHESIS IN THE LIGHT 



OF SOME NEW FACTS* 



H. A. SPOEHR 

 Desert Laboratory, Tucson, Arizona 



It is now more than one hundred and thirty-five years since 

 the fundamental principles of the cosmical function of green 

 plants was clearly recognized by Ingen-Houz, Priestley and 

 S^nebier. The classical researches of de Saussure on the gaseous 

 exchange of plants, which appeared shortly thereafter, still stand 

 as the most thorough and masterly which have appeared in the 

 history of the subject. Although the number of investigators 

 who have worked on the problem of photosynthesis since the 

 time de Saussure runs into the hundreds, and our knowledge 

 of the chemistry of the substances involved in the process has 

 been greatly extended, it cannot be claimed that we have as yet 

 taken any decided step toward an understanding of the chemistry 

 of the process based upon observation or rigid experiment. 



However, the work of Sachs in the sixties, on the function of 

 the chloroplasts, and the formation of starch therein, was the key 

 to the chemical aspect of the problem, and served as a great stim- 

 ulus to its further study. These researches established a direct 

 relation between the carbon dioxide absorbed by the leaf and the 

 starch formed therein. In fact, Sachs proved starch to be the 

 first "distinctly recognizable" product in the process of photo- 

 synthesis. What then, is the course and sequence of chemical 

 changes in the reduction of the simple compounds, carbon di- 

 oxide and water, to the highly complex starch? 



With the developments of organic chemistry it was but nat- 

 ural that attempts should have been made to explain the mode of 



*Substance of a paper read in the Symposium on Light Effects at the 

 meeting of the Botanical Society of America at Leland Stanford University, 

 August 4, 1915. 



THE PLANT WORLD, VOL. 19, NO. 1, 1916 



