FORMALDEHYDE FEEDING EXPERIMENTS 259 



against 19.2% at the beginning of the experiment, and 15.7% in the 

 starved control plants). Illumination had no effect on these results. 

 Formaldehyde poisoning of photosynthesis in Elodea begins at about 

 0.024% and leads to a complete suppression at 0.033%; the catalase 

 activity becomes affected in the same range of concentrations. 



Positive results were obtained also by E. and G. Nicolas (1922^' 2, 

 1923) in experiments on the effect of formaldehyde (0.01%) on the 

 growiih of peas. They noticed that, in the absence of chlorophyll, the 

 effect of formaldehyde was a purely toxic one. 



Bodnar, Roth, and Bernauer (1927) criticized Sabalitschka's experi- 

 ments for the lack of a direct proof that the difference in composition 

 between the formaldehyde-fed and starved plants was due to an assimila- 

 tion of formaldehyde rather than to the poisoning of respiration. (How- 

 ever, this objection does not apply to experiments in which the dry weight 

 after formaldehyde feeding was higher than at the beginning of the ex- 

 periment.) Bodnar and coworkers observed a significant increase in the 

 percentage of dry matter in formaldehyde-fed leaves ; although the respi- 

 ration of these leaves was strongly inhibited (by about 50%), this inhibi- 

 tion could account only for a small part of the observed difference in dry 

 weight. They found that no positive iodine test could be obtained with 

 formaldehyde-fed leaves of Tropaeolum, and suggested that sugars (and 

 not starch) are the only products of polymerization of formaldehyde by 

 leaves. 



That changes in water content did not affect the percentage of dry 

 matter in "formaldehyde leaves," was shown by the observation that 

 these leaves had a heavier dry weight and a larger sugar content than 

 did the fresh leaves before the experiment — and not only than the starved 

 control leaves. 



Bodnar and coworkers finally found that the production of reducing 

 sugars from formaldehyde is catalyzed also by leaf mash and dried leaf 

 powder, thus indicating the presence in this mash of a polymerizing 

 enzyme. No sugar was obtained from acetaldehyde with leaf mash; 

 neither was acetaldehyde assimilated by leaves (c/. page 261). BoiUng 

 destroyed the activity of leaf powder or leaf mash, indicating the de- 

 naturation of the enzyme. 



Experiments of West and Ney (page 273) indicate the possibility that 

 Bodnar's polymerization catalyst may be ascorbic acid. (However, the 

 West and Ney experiments dealt only with the polymerization of form- 

 aldehyde in alkaline solutions.) Results similar to those of Sabalitschka 

 and Bodnar and coworkers were also obtained by Godnev and Korshe- 

 nevski (1930) with leaves of Tropaeolum, Pelargonium, Tilia, and Urtica. 



These investigations by several independent workers appeared to 

 have settled definitely the question of the formaldehyde assimilation by 



