128 Prof. Keeble, Dr. Armstrong, and Mr. Jones. 



form red meri-quinoid compounds with the unchanged diamine — the so-called 

 Wurster salts. 



We have noted already that when hydroquinone is added to a mixture of 

 benzidine and oxydase in which the blue colour has been allowed to develop 

 the colour is discharged. It is not until all the hydroquinone has been 

 oxidised that the blue colour begins to return, the limiting factor being the 

 amount of hydrogen peroxide present. Most other phenols behave similarly 

 to quinol, but since their oxidation products are generally coloured, the blue 

 benzidine mixture becomes colourless for an instant only and then the solution 

 assumes a lavender, green, red, or brown hue, according to the phenol chosen. 

 This colour slowly changes, and as the benzidine blue returns it becomes 

 masked, and finally overpowered by the blue. 



The phenols experimented with include £>-cresol, orcinol, guaiacol, «- and 

 /3-naphthol, thymol, pyrogallol, resorcinol, phloroglucinol, saligenin, phenol, 

 methyl quinol, dimethyl quinol, etc. 



The list comprises certain phenols which usually do not give a colour 

 reaction with oxydase, e.g., methyl quinol. Even with a-naphthol the normal 

 lavender oxidation coloration is much more intense when produced in the 

 presence of other phenols. 



The behaviour of methyl quinol deserves special mention in that it affords 

 the basis for our hypothesis as to the production of serial colours in flowers. 

 With oxydase, methyl quinol gives no colour reactions ; but if a little 

 benzidine be added to the colourless solution the latter takes on a deep 

 and persistent carmine colour. The blue benzidine pigment acts catalytically 

 as an intermediary for the transmission of oxygen to the methyl quinol ; 

 that is, it may in this respect, and in this case, play the part of an organic 

 peroxide, and thereby achieve the oxidation of a substance (methyl quinol) 

 which resists the action of oxydase and hydrogen peroxide. 



The power of benzidine to transmit oxygen to methyl quinol and other 

 phenols may be illustrated by making use of the oxydase present in the 

 flowers, or other parts of plants. For instance, if the flower of a recessive 

 white P. sinensis be treated with benzidine and hydrogen peroxide, the petals 

 assume the blue-brown colour characteristic of the benzidine-oxydase reaction. 

 If, however, benzidine and methyl quinol be added together with hydrogen 

 peroxide a carmine coloration is produced. 



A similar oxygen transmitting power on the part of benzidine is exhibited 

 in the behaviour of the white flowers of Lychnis coronaria. Treated with 

 benzidine alone the petals become brown ; with a-naphthol they take on — 

 albeit with extreme slowness — a lilac or lavender colour. If, however, the 

 petals be treated with benzidine and a-naphthol they assume immediately a 



