142 On the Formation of Anthocyanin 



formation of anthocyanin is known to occur in connection with the 

 oxidation of aromatic compounds in the plant. The essential difference 

 between such reactions as lead to the formation of indigo, and those 

 which have been suggested for anthocyanin, lies in the nature of the 

 oxidase. In the former case the oxidase continues its function after 

 the death of the cell, but so far there is no evidence of anthocyanin 

 being formed in extracts from the plant', and it seems highly probable 

 that it is a process which is difficult or perhaps impossible to induce 

 under artificial conditions. The nature of the oxidases concerned will 

 be discussed later. 



Distribution of Pigment. 



The various organs of the plant in which anthocyanin may appear 

 can be enumerated as follows : 



Under normal conditions. 



(1) Veins, midribs and petioles of many leaves. Herbaceous stems 

 and the young stems of shrubs and trees. 



(2) Leaves of red-leaved species (Ainaranthtis, Goleus, etc.). 



(3) Leaves of red-leaved varieties of green-leaved types {Fagus, 

 Corylus, Beta, Atriplex, etc.). 



(4) Young developing leaves (Quercus, Rosa, Crataegus, etc.). 



(5) The older leaves of many plants {Fragaria, Aquilegia, etc.), and 

 sometimes the whole plant (many Umbelliferae, Galium aparine, etc.) 

 towards the end of the vegetative season. 



(6) Variegated leaves in which the chlorophyll is absent from 

 certain areas. 



(7) Flowers and ripe fruits. 



Under abnormal conditions. 



(1) Leaves which have been injured either mechanically or through 

 the attacks of insects and fungi. 



(2) Autumnal leaves. 



(3) Leaves exposed to low temperatures, such as evergreen leaves 

 in winter (Hedera Helix, Ligustrum vulgare, Mahonia sp., etc.). 



(4) Leaves exposed to drought. 



^ Except in so far as I have been able to induce a formation of colour in an extract from 

 Primula flowers by means of Horseradish peroxidase in presence of hydrogen peroxide. 

 Proc. Gamb. Phil. Soc. Vol. xv. 1909. 



