50 CARNEGIE INSTITUTION OF WASHINGTON. 



poisons on respiration and photosynthesis (O. Warburg), (c) dependence of 

 photosynthesis on certain oxygen pressure, (d) determination of photo- 

 synthetic efficiency (0. Warburg's Nutzeffekt). These and many older in- 

 vestigations are in accord with the theory of a direct interdependence of 

 photosynthesis and respiration which has been developed on the basis of work 

 carried out in this laboratory during the last two years. 



There seem to be two distinct sets of reactions which go to make up the 

 photosynthetic process. These two reactions are of unmistakably different 

 character and type. Under certain experimental conditions one of these 

 reactions is predominantly noticeable; under other circumstances, the prop- 

 erties of the second reaction are more apparent. One of these reactions is 

 photochemical, the other is an ordinary chemical reaction. The object of the 

 present researches is to establish the nature of these reactions and to determine 

 in what manner these two sets of reactions are coupled. It has, moreover, 

 been possible to differentiate these two steps of the photosynthetic process 

 experimentally and to apply the reasoning of recent theoretical physical de- 

 velopments to each of the steps. The conception of a possible primary pho- 

 tolysis of carbonic acid in the living organism has not only received no experi- 

 mental support but from the work of Willstaetter and Stoll and that carried 

 out in this laboratory becomes highly improbable. Moreover, by the calcu- 

 lations of E. Warburg on the basis of the Einstein law of photochemical equiva- 

 lent, the two simple reactions C02 = C+02 and 2 C02 = 2 CO+O2 are excluded 

 as photochemical primary reactions. 



Photosynthesis is not a simple photolysis of carbonic acid. There is required 

 an acceptor which reacts with the product of the primary light-reaction. 

 This acceptor is not carbonic acid, but is formed in a series of reactions into 

 which CO2 enters. The product of the primary light-reaction acts on the 

 acceptor to produce the secondary reaction. We have then in photosynthesis 

 first of all the formation of the acceptor and (1) the primary light-reaction and 

 (2) the secondary reaction. It is in the first of these reactions, the formation of 

 the photochemical acceptor, that the enzymatic or respiration process enters, 

 and this forms the basis of the interdependence of photosynthesis and respira- 

 tion. The reaction producing the acceptor is of the same chemical type and 

 apparently associated with respiratory activity. These studies have estab- 

 lished a quantitative relationship between the rates of respiration and photo- 

 synthesis. All factors which have been found to affect photosynthesis through 

 disturbances in the vital or protoplasmic activity of the plant exert their 

 influence through the respiratory process. Thus carbon dioxid is made the 

 acceptor in a photo-chemical reaction by being first altered in this process of 

 acceptor-formation, which step is in the nature of a coupled reaction. 



In view of the fact that the rate of photosynthesis follows so closely the 

 rate of respiration, the theory is proposed that these two series of reactions, 

 proceeding in opposite directions, are actually interdependent. This inter- 

 dependence may be either on the basis that the energy released in respiration 

 actually aids or is essential to one of the two reactions constituting the photo- 

 synthetic process, or the relation may be based upon the action of an enzyme 

 or catalyst which functions in both reactions. Into which of the two reactions 

 of photosynthesis the respiratory process meshes is still uncertain. However, 

 the contribution in energy which respiration could make would naturally be 



