256 INTERMEDIATES IN REDUCTION OF CO2 CHAP. 10 



However, Willstatter and Stoll (1918) who repeated these experiments 

 obtained negative results. 



Sabalitschka and Riesenberg (1924^) too, were unable to find form- 

 aldehyde in leaves. Even in leaves fed with formaldehyde, they found 

 only a small residue of the supplied material (in conformity with Fincke's 

 observations). 



Klein and Werner (1926) were the first to apply the method of 

 trapping to the formaldehyde problem, using Vorlander's reagent for 

 aldehydes (5,5-dimethyl-l,3-cyclohexanedione, also called "dimedon" or 

 "methone")- They saturated the plants (e. g., Elodea canadensis) with 

 dimedon, left it in the illuminated plants for several hours, and then 

 extracted again. The extract was distilled, the aldehyde-dimedon 

 compound crystallized and identified by its crystal form and melting 

 point. Formaldehyde quantities of the order of 10 mg. were isolated in 

 this way from 100 g. of plant material, illuminated for 5 hours with 

 7000-8000 lux. This is only 1-2% of the carbohydrate normally formed 

 by photosynthesis during the same period. Acetaldehyde, but no 

 formaldehyde, was found in plants which were kept in the dark, as well 

 as in chlorophyll-free tissues, and this was interpreted as a proof that 

 acetaldehyde is an intermediate product of respiration. 



The amount of formaldehyde trapped by dimedon in illuminated 

 plants decreased upon the addition of phenylurethane or potassium 

 cyanide — substances which inhibit photosynthesis. 



Klein and Werner's conclusions were confirmed by van Goor (1926) 

 and Pollacci and Bergamaschi (1929^-2, 1930), who also used dimedon. 

 Positive assays were also reported by Sommer, Bishop, and Otto (1933). 



On the other hand. Barton- Wright and Pratt (1930) found themselves 

 unable to reproduce Klein and Werner's experiments. Noack (1927) 

 called attention to the narcotizing effect of dimedon on the photo- 

 synthetic apparatus and suggested that the formaldehyde found by 

 Klein and Werner came from the photodecomposition of sugars (or other 

 organic compounds) rather than from photosynthesis. Noack's ob- 

 jections were disputed by Klein (1927) and by Pollacci and Bergamaschi 

 (1930), who asserted that formaldehyde can be identified under conditions 

 when photosynthesis is not appreciably narcotized by dimedon. 



Vorlander (1928) suggested that formaldehyde may come from the 

 oxidation of dimedon by "nascent" oxygen. Pollacci and Bergamaschi 

 (1930) answered that they were able to obtain a positive formaldehyde 

 test with dimedon also by first illuminating the leaves, and then adding 

 the reagent. However, this means an abandonment of the trapping 

 technique and return to direct analysis, which, in the case of formaldehyde 

 in plants, seems certain to fail; and in fact Klein and Werner have never 

 found any formaldehyde in preirradiated leaves. 



