PHOTOSYNTHESIS 27 



solution of carbon dioxide, the reaction taking place even in the 

 absence of any " sensitizer," but much more readily if some 

 " optical " or " chemical " sensitizer is present. Finally, these 

 investigators were able to duplicate all their results, using green 

 plant tissues, and to show that the temperature changes which 

 take place in a film of chlorophyll when it is exposed to an atmos- 

 phere of moist carbon dioxide in the sunlight are such as would be 

 required by the formation of formaldehyde and hydrogen peroxide 

 from carbonic acid. 



More recently, Ewart has showed that formaldehyde can com- 

 bine chemically with chlorophyll; from which fact, Schryver 

 deduces the theory that if for any reason the condensation of 

 formaldehyde into carbohydrates by the cell protoplasm does not 

 proceed as rapidly as the formaldehyde is produced by photo- 

 synthesis, the excess of the latter enters into combination with the 

 chlorophyll, and that if condensation into sugar uses up all the free 

 formaldehyde which is present in the active protoplasm, the com- 

 pound of formaldehyde with chlorophyll is broken down setting 

 free an additional supply for further sugar manufacture. Accord- 

 ing to this conception there are, in the chlorophyll-bearing proto- 

 plasm, riot only the agencies for the production of formaldehyde 

 from carbon dioxide and water and for the condensation of this 

 into carbohydrates, but also a chemical mechanism by means of 

 which the amount of free formaldehyde in the reacting mass may 

 be regulated so that at no time will it reach the concentration 

 which would be injurious to the cell protoplasm or fall below the 

 proper proportions for sugar-formation. This explanation affords 

 a satisfactory solution of the difficulty which formerly confronted 

 the students of photosynthesis, namely, the fact that free formal- 

 dehyde is powerfully toxic to cell protoplasm. Without some such 

 conception, it was difficult to imagine how the presence of formal- 

 dehyde in the cell contents, even as a transitory intermediate 

 product, could be otherwise than injurious. 



As a result of these studies, the nature of the chemical changes 

 which result in the production of formaldehyde as the first product 

 of photosynthesis, with the liberation of a volume of oxygen 

 equal to that of the carbon dioxide consumed, seems to be fairly 

 well established. 



