vn] THE FORMATION OF ANTHOCYANINS 107 



donnerait naissance a une matiere colorante rouge aux depens d'un 

 noyau chromogene de nature phenolique que possederaient tous les 

 tannins." Laborde was able to obtain red pigments from tannins by 

 means of certain chemical reagents and other treatment. 



The authors mentioned are only a selection of those who have believed 

 in the origin of anthocyanin from tannins, and the hypothesis held the 

 field for many years; we find it accepted in most text-books even of 

 fairly recent date (Pfeffer) 1 , though the evidence for its acceptance is 

 far from satisfactory. 



The next hypothesis of importance is that of Palladin (203, 210) 2 ; 

 he considers anthocyanin to be a member of a class of pigments which 

 he himself terms 'respiration pigments.' Although this hypothesis is 

 connected primarily with the function of anthocyanin, nevertheless 

 certain reactions are involved which justify its consideration in this 

 chapter. Since Palladin's views are largely based on the action, of 

 oxidising enzymes, some preliminary account of these substances may 

 not be out of place at this point. 



Certain organic compounds, such as guaiacum tincture, a-naphthol, 

 paraphenylene-diamine. benzidine, etc., are used as tests for oxidases 

 since they become oxidised to coloured products when treated with 

 oxidising enzymes under certain conditions. When the juice or water 

 extract of some plants is added for instance to guaiacum tincture, a 

 blue colour is immediately developed, and the plant is said to contain 

 a direct oxidase. Of other plants the juice or extract gives no colour 

 until hydrogen peroxide is added, and the plant is said to contain ah 

 indirect oxidase. A direct oxidase has been considered by many 

 authors to consist of a system, peroxide-peroxidase ; in the case of the 

 indirect oxidase, the peroxide is missing, and has to be supplied in the 

 form of hydrogen peroxide. If a systematic examination be made of 

 all natural orders as to their oxidase content, it will be found that the 

 direct oxidase reaction is characteristic on the whole of certain orders 

 or genera (Compositae, Labiatae, Umbelliferae, etc.), and the indirect 

 oxidase reaction of other orders (Cruciferae, Ericaceae, Crassulaceae, 

 etc.). It may be noted, in addition, that the plants giving the direct 



1 The Physiology of Plants, translated by A. J. Ewart, Oxford, 1900. 



2 Also Palladin, W., 'Das Blut der Pflanzen,' Ber. D. hot. Ges., Berlin, 1908, xxvia, 

 pp. 125-132. 'Die Verbreitung der Atmungschromogene bei den Pflanzen,' ibid. 

 pp. 378-389. 'Ueber Prochromogene der pflanzlichen Atmungschromogene,' ibid. 

 1909, xxvn, pp. 101-106. 'Ueber die Bedeutung der Atmungspigmente in den Oxyda- 

 tionsprozessen der Pflanzen,' ibid. 1912, xxx, pp. 104-107. 'Die Atmungspigmente 

 der Pflanzen,' Zschr. physiol. Chem., Strassburg, 1908, LV, pp. 207-222. 



