THE PHOTOSYNTHETIC PROCESS 55 



This last step is accomplished through the aid of the enzyme, 



catalase. 



All of the above theories have assumed the production of form- 

 aldehyde as a step in the photosynthetic process. Although 

 poisonous, it is quickly polymerized and is never present in large 

 quantities. Furthermore, many researches have shown that it 

 can be used by the green plant. Grafe (1911) showed that green 

 seedlings grown in an atmosphere containing formaldehyde with- 

 out carbon dioxide increased in weight when grown in the light, 

 as compared with similar plants grown in the absence of formal- 

 dehyde. This has also been supported by Miss Baker (1913). 

 But it should be added that all the experiments carried on to 

 show that plants can use formaldehyde are valueless as far as 

 the question at hand is concerned if carried on in the light. 

 Under these conditions the formaldehyde may be first oxidized 

 to formic or carbamic acid and then used by the plant in 

 the normal manner. Such experiments to be of value must 

 be performed in the dark, and have been, in fact, by Jacobi 

 (1919), Sabalitschka (1924), Bodnar (1927), and others, all of 

 whom agree that the plant does increase in dry weight under 

 these conditions. 



It has further been demonstrated that plant cells containing 

 chlorophyll will give an aldehyde test if exposed to light and carbon 

 dioxide while the cells of fungi do not. Formaldehyde has been 

 commonly found in distillate from green leaves, but it has also 

 been found in distilled hay, where there is no photosynthesis. It 

 is not certain from these experiments, then, whether the alde- 

 hyde is produced in photosynthesis or whether it is a decomposition 

 product. 



Bach had demonstrated that formaldehyde could be produced 

 in vitro from carbon dioxide and water in the presence of sunlight 

 provided that some sensitizer or catalyzer was present, but this 

 entire question as to whether or not photosynthesis was a vital 

 process was reopened by Usher and Priestley (1906-1911), who 

 removed chlorophyll from the leaf, spread it out in thin films of 

 gelatin, and exposed it to the light. A formaldehyde test was 

 easily obtained at the end of an hour, but at the same time the 

 chlorophyll was decolorized indicating decomposition, which 

 would indicate that the aldehyde found was not formed from a 

 photosynthetic action but as a decomposition product of the 



