M. Wheldalb 151 



most anthocyanin produce the greatest quantity of brown pigment. 

 Secondly, when fully pigmented flowers of the type in any species 

 (cultivated spp. of Chrysanthemum, Petunia and Pyrethrum) give a 

 strong oxidase reaction, tinged or less intensely coloured varieties 

 frequently give a less strong reaction, which may indicate that some 

 part of the oxidising mechanism has been lost from the varieties, as 

 I have previously suggested (19) for Lathyrus and Matthiola. 



On the other hand, very many anthocyanic plants give no direct 

 action withguaiacum, although nearly all living tissues give an indirect 

 action (i.e. after addition of hydrogen peroxide). It is possible that the 

 direct action is inhibited in these cases by some strong reducing sub- 

 stance in the plant. It is also more than probable that anthocyanin 

 oxidases are of a nature totally different from those connected with 

 respiration pigments and may, many of them, not react with guaiacum. 

 For the present no other explanation appears available. 



Some work on oxidising enzymes has been recently published by 

 Moore and Whitley (12). These authors do not support the hypothesis 

 of Bach and Chodat, i.e. that an oxidase consists of a mixture of two 

 enzymes, an oxygenase which acts upon certain substances in the plant 

 forming peroxides and a peroxidase which transfers the additional 

 oxygen atom from the peroxide to other bodies. 



When both enzymes are present, the plant extracts have a direct 

 blueing action on guaiacum, but when the peroxidase exists alone, 

 hydrogen peroxide must be added before blueing results (indirect 

 action). 



Moore and Wliitley suggest that only one enzyme — peroxidase — is 

 involved in the process and that the blueing, to a greater or less degree, 

 of guaiacum by plant extracts, is due to the existence of more or less 

 organic peroxide in the tissues and that no special enz^'me involved in 

 the formation of peroxide can be detected. 



This point of view greatly simplifies the conception of oxidation 

 processes. I am nevertheless of the opinion that peroxide formation in 

 the plant may be controlled by an enzyme, though it may not be pos- 

 sible to extract this substance and to obtain an expression of its activities 

 under artificial conditions. 



Since, moreover, the presence of organic peroxides in plants is 

 directly connected with the appearance of post-mortem pigments, it 

 must follow that the metabolism of this class of plants differs in some 

 fundamental respect from that of others; and in my opinion such a 

 constitutional diff'erence may quite well involve the existence of at 

 least one special enzyme. . '. 



