On the Function of Chdorophyll . 



13 



may show a faint trace of formaldehyde, but no reduction with Fehling's 

 test.* Apparently, in darkness, a feeble oxidation of xanthophyll may take 

 place as well as of chlorophyll. Chlorophyll, therefore, combines with carbon 

 dioxide when present in a saturated watery solution in darkness, forming 

 xanthophyll and a colourless waxy solid. In ligbt, the same action takes 

 place more rapidly and readily, and even under negative pressure. The rapid 

 yellowing of grass leaves when cut fresh and heaped in masses is due to 

 this action of carbon dioxide on chlorophyll. If a quantity of grass leaves 

 is boiled and kept in a dense mass, in a few hours the post-mortem production 

 of carbon dioxide has destroyed nearly all the chlorophyll, and large amounts 

 of xanthophyll can be extracted, but very little chlorophyll. 



Xanthophyll, Carotin, and Carbon Dioxide. 



Experiments were made by exposing («) dry films of xanthophyll and 

 carotin in dry carbon dioxide, (b) watery solutions of xanthophyll, and watery 

 emulsions of carotin in tubes sealed after saturating and filling with carbon 

 dioxide. After a week's exposure the colour was unaltered, no evidence of 

 combination could be seen, no new products appeared, and the enclosed gas 

 consisted of pure carbon dioxide with occasionally a trace of nitrogen 



General Conclusions. 



The foregoing results indicate that the assimilation of carbon dioxide is 

 notja simple process, as represented by the equation C0 2 -f-H 2 = CH 2 + 2 , 

 in which chlorophyll merely absorbs the energy required, but is a very 

 complex one, in which two pigments at least and their derivatives take part, 

 and in which the equilibrium between the products and reacting substances 

 determines the direction in which the reactions may take place, while light 

 influences this equilibrium and strongly accelerates the tendency to oxidation 

 on the part of all the pigments concerned. 



According to Willstatter, amorphous chlorophyll is the methylphytyl ester 

 of the tricarboxylic acid, C3iH 29 X4Mg(COOII)3, or chlorophyllic acid, and has 



COOH 



the formula C 3 iH 29 ]S T 4 Mg^COOCH 3 . 



X COOC 20 H 39 



The phytyl radicle can be displaced. Thus Willstatter and Stollf found 



* Although a strong solution of formaldehyde gives a reduction with Fehling : s test 

 just like a reducing sugar, with a weak solution the slight excess of alkali on warming 

 converts the formaldehyde into methyl alcohol and sodium formate. Hence dilute 

 solutions of formaldehyde give Schiffs test and other sensitive tests, but do not give 

 Fehling's test. 



t ' Annalen,' vol. 378, p. 18 (1910). 



