'358 



Messrs. L Jorgensen and F. Kidd. 



As to the production of an aldehyde on oxidation, it has been shown 

 above that, as far as chlorophyll is concerned, formaldehyde is only 

 produced at a late stage in the process of oxidation after bleaching of the 

 chlorophyll has taken place. It is thus a purely secondary product, arising 

 probably from the phytol which has been split off from the chlorophyll 

 molecule. 



c. Theory of Ewart. 



It is obvious from Ewart's paper (1) that he was not acquainted with the 

 work described in Willstatter's book (13), and it is clear that the method of 

 extraction Ewart employs, which he calls a modification of Willstatter's, will 

 not give pure chlorophyll. It is significant also from the description of 

 his " pure " pigments that they have properties different from those of 

 Willstatter, for instance, with regard to solubility. Also the formula for 

 chlorophyll given by Ewart is that suggested by Willstatter in earlier 

 papers, and is not the one put forward by Willstatter in his later book. 



Ewart is one of the first among recent workers to realise that carbon dioxide 

 assimilation is not a simple process, the first stage of which is represented by 

 the equation CO2 + H 2 = HCHO + O2, but a complex one in which at least 

 two pigments and their derivatives take part. However, it is clear that the 

 theory advanced by Ewart is not sufficiently supported by experimental 

 evidence. His main hypothesis is that carbon dioxide and water combine 

 with the phytyl group to give xanthophyll and oxygen. A portion of this 

 oxygen is then used to oxidise the xanthophyll into phytol, hexose sugars 

 and formaldehyde, while the remainder is excreted from the chloroplast. The 

 formaldehyde is then polymerised to hexoses either by contact with the 

 chlorophyll or by dilute alkali in the protoplasm around the chloroplast. 



Without entering into any detailed discussion of Ewart's hypothesis 

 attention must be drawn to the fact that in our experiments we have never 

 been able to obtain xanthophyll in a system containing chlorophyll, carbon 

 dioxide, and water, but we have obtained a yellowish-green substance which 

 we have identified as phaeophytin. One is almost forced to assume either 

 that Ewart's chlorophyll contained xanthophyll, or that the yellow substance 

 he obtained was phaeophytin. Unfortunately Ewart does not state on what 

 evidence he relied for the identification of his xanthophyll. 



In regard to Ewart's hypothesis of the re-formation of chlorophyll from 

 xanthophyll it has to be remembered that the magnesium-free derivatives of 

 chlorophyll very easily take up certain other metals and form a colour 

 complex resembling that of chlorophyll; even the small traces of metals 

 contained in the walls of glass vessels are sufficient for this. Thus 

 Willstatter was able to test for the presence or absence of zinc in glass 



