THE THEORIES OF PHOTOSYNTHESIS 9 



verely criticised^^ as not giving reliable results. Pollacci/' also 

 obtained aldehyde reactions in the distillate from illuminated 

 leaves ; these reactions were not obtained from leaves kept in the 

 dark, without CO2, nor from chlorophyll-free parts. The largest 

 number of investigations have been made by means of ii icro- 

 chemical methods, using the various color reactions as indica- 

 tion for the presence of formaldehyde. The difficulties of this 

 method are undoubtedly very great, as in but very few cases are 

 the tests sufficiently intense, so that it usually comes down to 

 distinguishing between various shades and colors produced by 

 other aldehydes and related substances present in the leaf. 

 Nevertheless, PoUacci, Grafe, Kimpflin,!^ Gibson^^ and others 

 have reported the presence of formaldehyde in illuminated 

 leaves. However, recently it has been found that there are a 

 number of substances present in the leaf which produce formal- 

 dehyde in the light quite independently of the reduction of car- 

 bon dioxide. Warner^" has found that chlorophyll films, under 

 the action of the oxygen of the air, produce formaldehyde in the 

 light. So also, Wager^i has shown that chlorophyll extracts, un- 

 der the influence of light, yield formaldehyde, and that the 

 bleaching of chlorophyll is not a result of the activities set up by 

 photosynthesis as suggested by Usher and Priestley. This, of 

 course, still admits the possibility that the carbon dioxide is 

 taken into the chlorophyll molecule, which then by photolysis 

 yields formaldehyde. The writer^^ has also found that a number 

 of organic acids which are known to be very common components 



" Fincke, H., Nachweis von Formaldehyd in den Pflanzen. Biochem. Zeit- 

 schr. 52 : 214-25, 1913. 



'' PoUacci, G., Intorno alia presenza dell aldeide formica nei vegetali. Atti 

 del R. isti. bot. dell'univ. Pavia, 6: 27, 1899. Atti Acad, dei Lincei, 1907. 



^^ Kimpflin, G., Presence du menthal dans les vegetaux vertes. Compt. rend. 

 144: 148-50, 1907. 



1' Gibson, R. J. H., Photoelectric Theory of Photosynthesis. Ann. of Bot. 

 22: 117-20, 1908. 



^^ Warner, C. H., Formaldehyde as an Oxidation Product of Chlorophyll Ex- 

 tracts. Proc. Roy. Soc. 87: B, 378-85, 1914. 



21 Wager, H., The Action of Light on Chlorophyll. Proc. Roy. Soc. 87: B, 

 386-407, 1914. 



2- Spoehr, H. A., Photochemische Vorgiinge bei der diurnalen Entsaurung der 

 Succulenten. Biochem. Zeitschr. 57:95-111, 1913. 



