Plant oxydases and the chemical interrelationships of colour- varieties. 465 



To proceed further, these oxydases are perhaps engaged normally 

 in oxidative metabolism. A local difference of metabolism, resulting 

 in a lessened reducing capacity of the tissues, such as we find in the 

 flower, ripening fruit and developing shoots, or a more general 

 disturbance, such as accompanies autumnal colouring, leads either to 

 a local or a general production of the normal oxidative product of 

 these oxydases — anthocyanin. Artificially the same result may 

 be obtained by feeding the plant with carbohydrates as Overton^) 

 and Katie-) have shown; alow temperature, also, will increase 

 tingeing in flowers, for example, certain varieties of Primula. Piosa, 

 which are nearly white when kept under warmer conditions. But 

 the more serious derangement due to death and injury leads to the 

 formation of such abnormal products as the post-mortem pigments. 



There is some experimental evidence in favour of this view. 

 I found all plants which became brown on autolysis, to be antho- 

 cyanic. Moreover, among autumnal Chrysanthemums, the pure white 

 variety shows autolytic changes and gives the oxydase reactions to 

 a far less extent than the coloured varieties. The case of Dipsacus 

 also suggests that the oxydase may form diff'erent products under 

 diff'erent conditions; for Dipsacus leaves on autolysis at ordinary tem- 

 peratures rapidly turn brown and do not produce blue dipsacotin. 

 On the other hand, indigo is produced at ordinary temperatures; 

 hence we should expect autolysis to induce indigo formation and this 

 has been confirmed by Wal t h er -^j and Molisch for Polygonum 

 tindorium and other indigo plants. Further evidence is furnished 

 by MaUhiola*); flowers of this genus give some direct action with 

 guaiacum but no starch-iodide test. Certain varieties, 'hoary whites', 

 become tinged with red on fading; in cross-breeding, these 'hoary 

 whites' behave as anthocyanic forms. On antolysing, the white flowers 

 become perceptibly red. Hence, in this case, when the oxydase is 

 freed, the normal product of its activity, i. e. anthocyanin, is appa- 

 rently produced. 



As to why the oxydase activity is let loose in some species after 

 death, while in others it remains in abeyance, I can at present offer 

 no suggestion. It is more reasonable to postulate the existence of 

 inhibitors, in some cases affected by autolysis or injury, in other 

 cases, unaffected, than to suppose such a vital mechanism as oxydase 

 activity to be present in some species and absent from others. 



') Beobachtungen und Versuche über das Auftreten von rotem Zellsaft bei 

 Pflanzen. Pringsh. Jahrb. f. wiss. Bot. 1899. 



^) Beitrag zur Kenntnis der Bildung des roten Farbstoffs. Inauguraldissertation. 

 Halle a. S. 1905. 



•^) Zur Frage der Indigobildung. Ber. d. d. bot. Gesell. 1908. 



*) Saunders, Reports to Evol. Oomm. Roy. Soc, Vols. I, II, III. 



