88 PHOTOSYNTHESIS 



periods of illumination. It has been an exceedingly difficult problem 

 to separate these two reactions, proceeding, as it were, in opposite direc- 

 tions. It needs no further analysis to realize that even slight variations 

 in the respiratory ratio would affect profoundly the results of the photo- 

 synthetic ratio. It must be borne in mind that respiration is an exceed- 

 ingly complex process, the resultant of a series of reactions, some of 

 which lead to the synthesis of material necessary for the life of the plant, 

 others to end or waste products. Many of the latter are rich in oxygen 

 and are broken down only under certain conditions. So that the absorp- 

 tion of oxygen and liberation of carbon dioxide may be separated by 

 many intermediate reactions.*^ 



Unfortunately there exists in the literature a great deal of confusion 

 as to the manner of designating the photosynthetic and respiratory 



O Oo ,CO, ^ , 



quotients. The former has been written -zr:r-, 7^7;~» ^^'^'-'TS — ' these 



C02 . 



pages th e photosynthetic quotient will be designated by -— — , i.e. 



vol. COo absorbed , . . Oo ^, . 



: and similarly the respiratory quotient 7:77-. ihis 



vol. Oo emitted CO3 



will necessitate that in some of the quoted works the symbols must be 

 specially noted because they are given as they stand in the original pub- 

 lications. Bonnier and Mangin ■*- endeavored to separate the photo- 

 synthetic and respiratory processes and made a number of determinations 

 of the photosynthetic quotient under special conditions. In their pub- 

 lication there are a number of misprints and arithmetical errors, which, 

 however, it is difficult to correct on account of the lack of original ex- 

 perimental data. By means of the following four methods it was attempted 

 to separate the gaseous exchange due to photosynthesis and respiration. 

 These methods have been extensively used for this purpose, with little 

 further critical examination. 



1. — Comparison of the gas interchange in the dark and in light. The 

 rate of respiration is determined in the dark, and in the light the gas 

 interchange due to photosynthesis plus respiration is measured. From 

 this data it is possible to obtain the values for the changes in the com- 

 position of the gas surrounding the plant due to photosynthesis alone. 

 Thus, if in a given time c is the volume of carbon dioxide emitted in the 



, o O2 



dark, o is the volume of oxygen absorbed in the dark — = = r, the 



C V^vJ2 



respiratory quotient, and if in the same time Ci is volume of carbon dioxide 

 absorbed in the light, Oi is volume of oxygen emitted in the light, the total 

 carbon dioxide absorbed in photosynthesis is c + Ci and the total oxygen 

 produced, o + O], and the true photosynthetic quotient is 



"Spoehr, H. A., Carnegie Institution of Washington Pub. No. 287, 1-23 (1919). 

 *^ Bonnier and Mangin, Ann. Sci. not. Bot.. (7) 3, 1-44 (1886). 



