296 PHOTOSYNTHESIS 



The only cultures which showed a final increase in dry weight in 

 the light were those containing carbon dioxide ; where formaldehyde was 

 present the loss in final weight was less than without. Miss Baker showed 

 that formaldehyde had no effect on the respiration of the seedlings in 

 the dark, so that in all probability the smaller loss in dry weight in 

 the presence of formaldehyde cannot be ascribed to a retarded rate of 

 respiration. It is significant that in the dark formaldehyde does not show 

 this effect of a smaller loss of dry weight. The question arises whether 

 in the experiments of Baker, Grafe and others,''" in which there appears 

 to be a utilization of a small amount of formaldehyde in the light, these 

 cannot be interpreted on the basis that the formaldehyde is oxidized 

 in the light. Spoehr ^^ found that formaldehyde vapor is oxidized to 

 formic acid by air in sunlight. In the experiments just referred to, 

 were the plants actually utilizing formaldehyde or was it formic acid, and 

 is the fact that formaldehyde is less toxic in light to be explained on 

 the basis that in the light it is partially oxidized? 



More recently Jacoby has studied the effect of gaseous formaldehyde 

 on nasturtium leaves in the dark. He took two sets of leaves, one 

 exposed to an atmosphere of formaldehyde, the other in air ; after 24.5 

 to 32 hours the dry weight was determined and in six experiments the 

 formaldehyde cultures had a dry weight 1.7 to 5.4 per cent higher than 

 the controls. In a later paper Jacoby ^" reports experiments in which 

 oxygen was removed from the atmosphere containing the formaldehyde 

 and here also he concludes that the formaldehyde was fixed by the leaves. 

 Sabalitschka and Riesenberg ^^ have also reported an increase in sugar 

 and starch in leaves which were exposed to an atmosphere containing 

 formaldehyde in the dark. 



Contradictory and uncertain as nnich of the work on the feeding of 

 formaldehyde is, it seems to indicate that small amounts can be utilized 

 by the plant. The fact that it is so injurious to protoplasm naturally ex- 

 cludes the tolerance of high concentrations. Whether the formaldehyde, 

 if formed as an intermediate product in photosynthesis, is combined with 

 some other substance and thus is less toxic, or in this form undergoes 

 condensation to sugars more easily, it is of course impossible to say. 

 There is, however, no chemical evidence which would support such an 

 opinion. The fact that formaldehyde may be used by the plant to form 

 sugars may be regarded only as supplementary evidence for the formalde- 

 hyde theory, for there are many other substances from which the plant 

 can manufacture sugar, and apparently far more easily than from formal- 

 dehyde. 



'"Ewart, Proc. Roy. Soc, 80 B, 30 (1908). Usher and Priestley, ibid., 78 B, 

 321 (1906). 



"Spoehr, Plant World, 19, 15 (1916). 



"^Jacoby, Biochem. Zeit., 101, 1 (1919-1920) ; 128, 119 (1922). 



*^ SabaHtschka and Riesenberg, ibid., 144, 545 (1924). Boitreux, Conipt. rend, 

 soc. biol., 83, 737 (1920). 



