The Formation of the Anthocyan Pigments of Plants. 119 



formed independently of the plastids in special vacuoles of the cytoplasm. 

 The former are called plast pigments and the latter sap pigments. In the 

 mature cell the sap pigments occur in solution with the general cell sap, and 

 hence they are referred to sometimes as the soluble sap pigments. They 

 occur in two series, the soluble yellow pigments (see p. 115) and the so-called 

 anthocyan pigments. Evidence has been given already (p. 117) to show that 

 the soluble yellow pigments are to be regarded as flavone derivatives, and 

 that they are related with the red and blue anthocyan pigments. 



Of the plast pigments, two series also occur. One comprises the yellow 

 and red carrotene pigments, together with the oxidised derivatives of the latter, 

 the xanthophylls. The other series includes the chlorophyll pigments. Of 

 these pigments, carrotene (a hydrocarbon) contains C and H, xanthophyll, 

 the soluble yellow sap pigment, and the anthocyans contain C, H, 0, and 

 chlorophyll, like haemoglobin and the animal melanins, contains N in 

 addition to these elements. 



It is known that the melanins of animal tissues are produced by the 

 action of tyrosinase on chromogens. We show now that pigments containing 

 nitrogen are formed readily by the action of plant enzymes on the glucosides 

 which occur in plants. Hence it is probable that the formation of such 

 nitrogen-containing pigments occurs normally in the living plant. 



Two recently published researches of Chodat have important bearings on 

 the mode of pigment formation in plants. In the one research, Chodat* 

 proves that, when a vegetable oxydase acts on glycine, carbon dioxide, 

 formaldehyde, and ammonia are produced. In the other, he demonstrates 

 that, when p-cresol is oxidised by oxydase in the presence of an amino- 

 compound, a series of coloured substances is produced, the colours of which 

 depend on the nature of the amino-compound. 



We have confirmed the accuracy of Chodat's conclusions and have applied 

 them to an investigation of the behaviour of certain glucosides, arbutin, 

 methyl arbutin. and others, when acted on by plant enzymes. 



Arbutin and methyl arbutin are distributed widely among species of the 

 genus Pyrus and also among the members of the Ericaceae and certain other 

 natural orders. When hydrolysed by emulsin, arbutin and methyl arbutin 

 yield respectively quinol and its mono-methyl derivative. Inasmuch as 

 emulsin usually contains a small quantity of oxydase, hydrolysis is 

 accompanied by a darkening of the solution owing to the oxidation of the 

 quinol. It has been suggested by Bourquelot and Fichtenholz that the 

 natural blackening which takes place in the fallen leaves of many species of 

 Pyrus is due to the oxidation of quinol. 



* ' Arch. Sci. Phys. Nat.,' 1913, vol. 35, p. 140. 



