372 PHOTOSYNTHESIS 



of the experimental data upon which this theory was hased have been 

 found to be faulty, because impure preparations of chlorophyll were used. 

 Wurmser's ^^ observations on the photo-oxidation of chlorophyll also 

 indicate that in the plant the chlorophyll is protected against photo- 

 oxidation. 



The opinion that photo-oxidation plays a role in photosynthesis has 

 also been developed by Noak.*'^ He regards chlorophyll as a photo- 

 dynamically active substance which due to its fluorescence has the power 

 of forming a peroxide from oxygen and an acceptor under the influence 

 of light. The mode of reduction of carbonic acid is. however, not eluci- 

 dated. Noak showed that benzidine in the presence of chlorophyll is 

 oxidized in the light, in solutions as well as in the chloroplasts. Noak, as 

 well as Woker '^'^ stress the significance of peroxide formation under the 

 influence of light and it is conceivable that peroxides may play an im- 

 portant part in the photosynthetic reactions. The nature of these peroxides 

 is still undetermined, but these may be either of the type of Willstatter 

 and StoU's formaldehydeperoxide, an isomeric form of carbonic acid, 



H O 



1/ 

 = C(0H)2 >HO — C .or 



\ 



O 



other peroxides which may split off oxygen or themselves act as re- 

 ducing agents. When a fluorescent substance produces a photodynamic 

 action it is apparently destroyed. This, in the case of photosynthesis, 

 would lead to the destruction of chlorophyll. Whether the idea of a 

 continuous destruction and reformation of chlorophyll during photosyn- 

 thesis is tenable is doubtful. 



Perhaps the strongest argument against the theory that chlorophyll is 

 decomposed during photosynthesis is offered by the investigations of 

 Willstatter and Stoll.^^ They made careful determinations of the amount 

 of chlorophyll in various leaves before and after very active photosyn- 

 thesis. There were no differences observed in the amount of chlorophyll. 

 This is illustrated in Table 47. These investigators established this fact 

 in an extended series of experiments. 



Willstatter and StoU also showed that there was no appreciable con- 

 version of one chlorophyll component into the other during the course of 

 photosynthesis. At least, after very active photosynthesis the ratio of 

 chlorophyll a and h in the leaves is very nearly the same as before illumina- 

 tion. On the other hand, a change in the amounts and ratio of the two 

 yellow pigments, carotin and xanthophyll, was observed after active photo- 



" Wurmser, "Recherches sur rassimilation," p. 18. 



"Noak, Zeit. Bot., 17, 481 (1925) ; 13, 389 (1921) ; Review of Warburg, ibid., 

 12, 273 (1920). 



«* Woker, Arch. ges. Physiol, 176, 11 (1919). 



"Willstatter and Stoll, "Untersuchungen ii. Kohlensaureass.,'" pp. 11-166. 



