M. Wheldale ■ 141 



This appearance of pigment on autolysis is especially frequent 

 among genera of the Labiatae, Boraginaceae, Scrophulariaceae and 

 Umbelliferae, though it is also generally characteristic of some of the 

 genera in most Natural Orders. Often, as in the Ranunculaceae, this 

 phenomenon is peculiar to all species of certain genera {Anemone, 

 Hellehorus, Clematis, TroUius, Caltha and Aconituvi), which rapidly 

 yield brown pigment on autolysis in chloroform, whereas all species of 

 other genera {Ranunculus, Paeonia, Aquilegia and Thalictrum) give no 

 colour in the same time of exposure. 



It is probable that the processes involved in the formation of post- 

 mortem pigments are in all cases analogous to those known to take 

 place in the production of indigo. The aromatic chromogen, from 

 which the pigment is produced, is combined with sugar in the form of 

 a glucoside in the living cell. In such a form the chromogen cannot be 

 attacked by the oxidase. When the cell is subjected to chloroform 

 vapour, the velocity of the hydrolytic reaction is accelerated and the 

 whole of the glucoside is split into chromogen and sugar. The free 

 chromogen is then fully oxidised by the oxidase. 



Accoi'ding to the view held by Palladin(14), these aromatic glucosides, 

 together with the glucoside-splitting and oxidising enzymes, form an 

 important system in the plant for the purpose of oxidising respirable 

 materials, and the post-mortem pigments have been termed by him 

 " respiration pigments." In the living unpigmented cell, the processes 

 of oxidation, reduction and the glucoside splitting reaction are so 

 balanced that no free pigment appears. To quote Palladin(l.T): — 

 " Einer sparsamen Hausfrau vergleichbar, halt die Zelle die Chro- 

 mogene verschlossen und verausgiebt sie in geringen Mengen fiir 

 Oxydationsprozesse. Die Ausgabe wird durch ein die Prochromogene 

 spaltendes Enzyme besorgt." 



To the chromogen in combination with sugar as a glucoside, 

 Palladin has applied the term " prochromogen." He also includes 

 anthocyanin among the respiration pigments, but does not offer any 

 very definite explanation of the appearance of anthocyanin in various 

 plant organs. 



I am inclined to believe that anthocyanin itself has no direct 

 respiratory function in that it is absent from albino varieties, which do 

 not appear to suffer from the loss of j)igment, since they grow and 

 reproduce quite as vigorously as the pigmented types. 



From the description of enzyme actions given above it will be .seen 

 that a series of reactions such as I have supposed to take place in the 



