130 



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



agency of that factor, and, in consequence, the blue pigment is reduced to the 

 state of a colourless chromogen. The observations recorded on p. 126 lend 

 additional support to this hypothesis. It is there observed that various 

 phenols intensify, though they may not change, the colour produced by the 

 action of oxydase on artificial chromogens. On the practical side it is also 

 known that intensifiers of pigment exist, that they possess the power of 

 converting a pale into a deep shade, and that they behave each as a unit 

 character. On our model it seems reasonable to assume that an intensifier is 

 a phenolic or similar substance, and that the factor for an intensifier means 

 the power of the cell to produce that substance. 



Lastly, on the basis of this hypothesis we have a plausible explanation of 

 the fact that many oxydase reagents, though they give good " bundle " 

 reactions, fail to reveal the presence of oxydase in the epidermis. The 

 vascular tissues contain considerable stores of oxydase and oxygen-carrier, 

 and hence, through the agency of the carrier, oxygen is transferred to 

 a-naphthol or similar " artificial chromogen." The epidermal tissue contains 

 only a small quantity of the carrier of oxygen, and hence, in spite of the 

 presence of oxydase, a-naphthol and similar artificial chromogens remain 

 unoxidised in this tissue. 



Conclusions. 



1. The pale yellow sap colour of the petals of the wallflower is a mixture 

 of hydroxyflavone glucosides. The glucoside mixture is hydrolysed readily 

 by heating with mineral acids and more slowly by emulsin of almonds. The 

 hydrolysed product if reduced and subsequently oxidised yields a red 

 pigment. 



2. The fact that flowers containing similar soluble yellow pigments may be 

 caused, by suitable chemical treatment, to yield a red pigment, suggests that 

 red mutations should be of possible occurrence in such species. 



3. The formation of pigments, as the result of oxidation by oxydase of the 

 hydrolysed products of glucosides, is determined by the presence of amino- 

 compounds and is of very general occurrence. The behaviour of the glucoside 

 arbutin (see p. 121) makes it probable that many of the pigments and odorous 

 substances formed during the ripening of fruits arise as results of reactions 

 of this type. 



The pigments of plants may be classified provisionally as follows : — 



I. Plast Pigments — 



a. Chlorophyll pigments contain C, H, 0, N 



b. Carrotene contains C, H 



c. Xanthophyll (oxidised carrotene) contains C, H, 



