Oxidation of Rhodoj^hyllin. 197 



leaves exposed to light. Brown leaves of Salix Babylonica were 

 collected in quantity and boiled and pressed repeatedly until all 

 the soluble tannins were removed. They were then washed with 

 absolute alcohol, and extracted with hot absolute alcohol. 



The liquid was filtered, concentrated and cooled and refiltered. 

 The brown waxy solid removed consisted partly of phaeophytin. 

 Ether was added to the alcohol and then salt. The reddish yellow 

 ethereal layer contained all the pigment. After washing with 

 water and drying with sodium sulphate, it was evaporated. The 

 residue was extracted with methyl alcohol, leaving a white waxy 

 solid undissolved. To the liquid, alcoholic potash was added, and 

 after heating, it was filtered. On standing, shining red platelets 

 with a steely blue shimmer of potassium rhodophyllin separated 

 out. 



Yellow leaves picked off the tree and kept in darkness for three 

 days turned brown, as in fallen leaves, so that the change is not 

 necessarily due to light. They yielded, however, xanthophyll 

 largely on extraction and rhodophyllin only in small amount. 



Rhodophyllin was also obtained from the brown autumnal 

 foliage of the English oak. When these are red in colour erythro- 

 phyll is present- in the cell sap, but it soon fades, leaving them a 

 pure brown colour. The colour of such leaves is due to several pig- 

 ments of which the erythrophyll fades first, then the xanthophyll, 

 then the rhodophyllin and the permanent brown colour is due prac- 

 tically wholly to oxidized tannin compounds. 



The evolution of oxygen from etiolated plants. 



It appears from the foregoing that etiolated leaves contain 

 carotin, a little xanthophyll, and a nearly colourless waxy solid 

 rich in magnesium, which is either glaucophyllin, or is related to 

 it. Carotin appears to be the first pigment formed in the construc- 

 tion of chlorophyll, and presumably it is produced at the expense 

 of carbo-hydrate or of hydrocarbon food materials. The relative 

 amounts of carotin and xanthophyll in etiolated parts may depend 

 upon the relative activities of oxidase and reductase enzymes re- 

 spectively. 



When an etiolated plant turns green in light, it seems reasonable 

 to suggest that the carotin undergoes photo-oxidation, •! liberating 

 formaldehyde, which is rapidly polymerized, and that the bleached 



1 111 the case of plants able to develop chlorophyll in darkness, an oxidase enzvme could 

 produce the same effect. 



