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SCIENCE PROGRESS 



viously mentioned. Making use of plants of known pedigree 

 they established the occurrence of various kinds of white flowers, 

 such as the type described above in which an inhibitor exists, 

 and that in which an active oxidase is found, unaccompanied 

 by a chromogen. They have also explained the restoration of 

 colour to a flower decolorised in alcohol. For example, the 

 brown wallflower has yellow plastids and a red anthocyanin 

 sap pigment. Alcohol extracts the former, and reducing sub- 

 stances present in the cell destroy the latter. On addition of 

 water, however, the oxidases again become active, and produce 

 the red pigment from the chromogen by oxidation. So the 

 flower then appears red, and not brown, as the yellow is not 

 restored. The author has examined the flowers of about thirty 

 varieties of Iris by means of benzidine and a-naphthol, and on 

 the whole the results obtained follow closely those of Keeble, 

 Armstrong and Jones. The presence of a powerful inhibitor in 

 many of the flowers presents features of interest, and the restora- 

 tion of the anthocyanin pigment after decolorisation in alcohol 

 is only brought about in the more deeply pigmented forms. 

 The pigment is diffusible, and unless the chromogen is also 

 diffusible the supply ought not to diminish. That it does 

 diminish would appear to point to production of pigment from 

 a chromogen derived from a colloidal pro-chromogen by hydro- 

 lysis. In this connection it is noteworthy that in the red algae 

 there exists a plastid pigment which is seen to be bright red 

 when other pigments have been extracted from the plastids by 

 alcohol. It behaves like an indicator, being red with acids, 

 colourless with alkalis. Though the cell sap is faintly acid, it 

 is decolorised by boiling, apparently going into solution, but 

 addition of an acid restores the colour, probably by hydrolysis 

 of a chromogen. This the author hopes to examine further. 1 



1 Since this paper was written, the above explanation of Keeble and Armstrong 

 as to the restoration of colour in petals has been severely criticised by Wheldale 

 and Bassett (Proc. Roy. Soc. 1914, B. 87, 300). These authors regard it as due to 

 ionisation changes, such as are undergone by phenolphthalein, rather than as an 

 oxidase action, though they are of the opinion that the enzyme is concerned with 

 the production of the anthocyan pigment in the first instance. The author has 

 satisfied himself as to the validity of the major part of this criticism by repeating 

 the work on Iris petals. It must, however, be pointed out that hydrogen peroxide 

 frequently behaves as a reducing agent ; this Wheldale and Bassett have over- 

 looked. The restoration of colour in the red algae is also brought about by acids, 

 as mentioned above. 



