THE PHOTOSYNTHETIC PROCESS 57 



synthesis. As a sample of the less fantastic of these " arm-chair" 

 chemical equations are presented those of Gordon (1929), who has 

 proposed the following scheme : 



6C55H7o0 6 N4Mg+6H 2 = 6C55H720 5 N4Mg+602 



chlorophyll B chlorophyll A 



6C55H7205N4Mg+6C02 = 6C55H 7 o0 6 N 4 Mg-r-C 6 Hi 2 6 . 



chlorophyll A chlorophyll B sugar 



Spoehr and McGee (1924) have suggested that the carbon 

 dioxide unites with protein in the leaf as carbon dioxide in the 

 blood unites with hemoglobin. From this protein compound 

 the carbohydrates are split off without the intermediate steps 

 of formaldehyde or carbonic acid. This is one of the few 

 modern theories which does not presuppose the formation of 

 formaldehyde and, although interesting, is not so promising as 

 some others. 



Hypothesis of Willstatter and Stoll— These men, who did so 

 much to clarify the chemistry of chlorophyll, also tried to explain 

 (with not so much success, however) the function of chlorophyll. 

 According to them, photosynthesis takes place in four successive 

 steps: 



1. The first step is the union between the carbon dioxide, 

 water, and chlorophyll to form a chlorophyll-carbonic acid com- 

 pound. This is a chemical process and as such does not require 

 light. It, consequently, has a temperature coefficient of 2 or 

 more. 



2. In the next step, the energy absorbed from the sunlight 

 causes a rearrangement of the molecules in this compound so that 

 some sort of organic peroxide is formed. This is the photochemical 

 stage of the process for which light is necessary and which has a 

 temperature coefficient of 1. 



3. From this organic peroxide, formaldehyde is split off by 

 means of enzymes, thus forming formaldehyde, chorophyll, and 

 oxygen. It also is a chemical reaction with a temperature coeffi- 

 cient of at least 2. As an argument in favor of the formation of 

 formaldehyde, they called attention to the fact that according to 

 the ordinary chemical equation, C02+H 2 = CH 2 0+02, the 

 C0 2 :0 2 ratio is 1, while if formic acid were formed (2C0 2 +2H 2 

 = 2HCOOH+0 2 ), the ratio would be 2. But Kostychev has 

 pointed out that if sugars are the final product, they can be 



