FORMALDEHYDE FEEDING EXPERIMENTS 257 



Thus, the results of formaldehyde assay in illuminated plants remain 

 contradictory and inconclusive. 



2. Formaldehyde Feeding Experiments 



The second method used in biochemistry to identify the intermediates 

 is the "substitution test." One could think of testing Baeyer's theory 

 by investigating whether the plants would accept formaldehyde instead 

 of carbon dioxide as a material for the synthesis of sugars. 



Experiments of this type have been attempted for over fifty years; 

 but many circumstances conspired to make the results indecisive. In 

 the first place, it was known even in Baeyer's time that formaldehyde 

 is poisonous to plants. Consequently, Loew and Bokorny (1887), who 

 were the first to attempt the "formaldehyde feeding" of plants, used 

 methylal, OC(OCH3)2, as a nonpoisonous substitute (they assumed that 

 it hydrolyzes in the cells to formaldehyde and methyl alcohol). They 

 observed that certain algae, Spirogyra, for example, can grow in the dark 

 in methylal solutions. Bokorny (1888) found that starch is produced 

 by the algae from methylal, but only in light. Later (1892), the same 

 author observed that sodium formaldehyde sulfonate, HOCH2S03Na, 

 is used by algae in the same way as methylal. Bouilhac (1901, 1902) 

 and Bouilhac and Giustiniani (1903) obtained similar results with the 

 Nostoc algae, both in methylal solutions and in weak solutions of form- 

 aldehyde, but again only in Hght. Treboux (1903) obtained completely 

 negative results in attempts to grow algae in formaldehyde or methylal 

 solutions in darkness. 



Bokorny (1908, 1909, 1911) found later that algae are less easily poi- 

 soned if the formaldehyde is in vapor form instead of solution; he found 

 under these conditions, a production of starch from formaldehyde by 

 illuminated Spirogyra. Grafe and Vortheim (1909), Grafe and Vieser 

 (1909), and Grafe (1911) observed that land plants, too, can stand 

 comparatively high concentrations of formaldehyde vapor (up to 1.3% 

 by volume) if their roots are protected, and are able to utilize it for the 

 production of organic matter. Similar conclusions were reached by 

 Baker (1913), who found that formaldehyde vapor is more poisonous 

 to green plants in light than in the dark, and by E. and G. Nicolas 

 (19221- 2) who observed that formaldehyde is less poisonous to green pea 

 plants than to seedlings not containing the green pigment. All these 

 results indicate that, in the presence of chlorophyll, formaldehyde 

 undergoes a photochemical decomposition which prevents poisoning. 

 This conclusion agrees with the observation of Fincke (1913) that plants 

 (or plant mash) rapidly destroy formaldehyde (cf. page 255). Whether 

 this disappearance is due to synthesis (polymerization to carbohydrates), 

 or to decomposition (e. g., oxidation to formic acid, as in experiments on 



