On the Function of Chlorophyll. 



11 



weighed 0'26 grm. It turned white in water, but was wholly insoluble in 

 water and contained no sugar. The gas from the tubes was passed into 

 water, which gave a distinct pink with Schiff's test. Apparently oxidised 

 carotin produces formaldehyde but no sugar or carbon dioxide. The amount 

 appears to be less than with chlorophyll or xanthophyll, but further quanti- 

 tative investigations are necessary on this point. The supply of carotin 

 obtained from the chlorophyll extraction was soon exhausted as the yield is 

 very small, but carotin extracted from carrots may be used in its place. It 

 also appeared to give off appreciable quantities of formaldehyde gas during 

 bleaching, while the bleached residue was practically insoluble in water, and 

 the watery extract either gave no reduction at all, or a doubtful trace with 

 Fehling's test. 



The Reduction of Xanthophyll to Carotin. 



Although the former differs from the latter simply in containing two atoms 

 of oxygen, it is less readily oxidised, and no oxidising agency tried was found 

 to convert carotin into xanthophyll. According to Palladin, however,* 

 carotin is converted by an oxidase into xanthophyll, while a reductase enzyme 

 carries out the reverse change. Using a variety of plant oxidases, including 

 those of the carrot, apple, potato and parsnip, I have not been able to produce 

 any conversion of carotin into xanthophyll using finely divided carotin and 

 watery or glycerine oxidase extracts. Under water in fact carotin oidy 

 oxidises slowly and with difficulty even when exposed to sunlight. 



The conversion of xanthophyll into carotin is, however, readily produced 

 by adding magnesium dust or zinc dust to a watery solution of xanthophyll 

 in darkness. In the first case nascent hydrogen acts as the reducing agent 

 and the action is rapid, being completed in one to a few hours. The zinc 

 acts slowly (2 — 3 clays). On filtering, a clear liquid comes through, and after 

 washing the residue with absolute alcohol, petrol-ether dissolves out the 

 carotin, which when evaporated is insoluble in water, and has the usual 

 properties. 



The Combination of Carbon Dioxide ivith Chlorophyll. 



Tubes were lined with dry chlorophyll, sufficient water added to cover the 

 film, and a current of carbon dioxide passed through until the water was 

 saturated. The tubes were then drawn out and sealed while the gas was 

 passing through, leaving half the tube filled with gas. On exposing to sun- 

 light the rise of temperature causes bubbles of gas to separate on the film, 

 distorting it and making it form an irregular network adhering to the glass. 

 The bright green colour is lost. After a week the gas above had decreased 



* ' Ber. d. D. Bot. Ges.,' vols. 26a and 27 (1908 and 1909). 



