322 The Formation of the Anthocyan Pigments of Plants. 



examples the depth of colour obtained is very considerable ; in the case of 

 Chrysanthemum the colour change is only slight. 



All the flowers belonging to this class give the characteristic peroxydase 

 reaction with benzidine or a-naphthol solutions and hydrogen peroxide. 



2. White Mowers which contain a Peroxydase and a Chromogen. — This type 

 of white flower is illustrated by certain varieties of Dianthus caryophyllus 

 {e.g. var. " Mrs. Sinkins,") and of Dianthus barbatus (Sweet William), etc. 



These flowers on treatment with dilute alcohol, chloroform, etc., show no 

 development of colour, but the addition of H 2 2 causes a rapid formation of 

 pigment. In many flowers of this class colour is produced only locally in 

 the petal on the addition of hydrogen peroxide. On testing such a flower 

 with benzidine solution with the subsequent addition of hydrogen peroxide, 

 a peroxydase reaction is obtained only in these same localities. The 

 peroxydase is limited, therefore, to those areas that give a colour reaction 

 when treated with alcohol, etc., and hydrogen peroxide.* Whether the 

 chromogen, which contributes to the reaction occurring in alcohol is present 

 in the regions from which peroxydase is absent is as yet undetermined. 



3. White Flowers which contain a Peroxydase but no Chromogen. — The white- 

 flowered varieties of Plumbago capensis and Sioainsonia Tacsonia illustrate 

 a third type of white flower. 



No colour reaction is given after treatment with chloroform or similar 

 bodies even after the addition of hydrogen peroxide. Such petals, however, 

 give in every case a reaction with benzidine and hydrogen peroxide. 



4. White Flowers which contain no Oxydase or Peroxydase. — A fourth type 

 may perhaps be inferred from the behaviour of a white variety of Sweet 

 William investigated by Keeble and Armstrong, which was found to give no 

 benzidine reaction, direct or indirect, and was therefore assumed to lack 

 oxydase and peroxydase. The possibility of an inhibitor being present was 

 not overlooked, but was not investigated. Information as to the occurrence 

 of a chromogen in these flowers is also wanting. 



The interpretation suggested above of the behaviour of white flowers when 

 treated with alcohol, etc., is the most obvious and simple one, but it is fully 

 recognised that intermediate steps may occur of which no account has been 

 taken. 



In Lychnis coronaria, it may be that a chromogen, as such, does not occur 

 in the intact petals, but is split off from a body which one may term a 

 pro-chromogen, after the plasmatic impermeability has been destroyed by 

 treatment with alcohol. 



* In coloured varieties these same areas are often the only parts of the flower 

 containing pigment. 



