vi] INFLUENCING THE FORMATION OF ANTHOCYANINS 91 



by Wigand (136) as early as 1862, and the same idea has been revived 

 successively by Palladin (203), Wheldale (211, 212) and Combes (379). 

 That the process is controlled by a specific oxidase has been postulated 

 by Buscalioni & Pollacci (17), Mirande (365) and Wheldale (211, 212). 

 The actual dependence of the process on the presence of oxygen is 

 illustrated by the experiments of Mer (284), who mentions the fact that 

 leaves of Cissus do not redden under water, and in 1899 Emery (309) 

 noted that no colour is produced in submerged flowers. 



More definite experiments were performed by Katie (354), inciden- 

 tally, among a series of investigations primarily concerned with the effect 

 of culture solutions on the formation of anthocyanin. Leaves in certain 

 culture solutions of sugars, and other substances, were found to produce 

 anthocyanin, but if enclosed in vessels, from which all oxygen had been 

 removed by alkaline pyrogallol, no trace of colour was observed. Katie 

 also found that colour was less rapidly developed in air under reduced 

 pressure than in normal atmosphere. Also in certain culture solutions 

 an increased pressure of oxygen produced greater development of 

 colour. 



Still more elaborate investigations were made by Combes (379). 

 The experiments consisted in analysing the gaseous exchange of red 

 and green leaves under similar conditions. Leaves were employed 

 in which reddening had taken place and was proceeding from different 

 causes, as for instance: leaves of Ampelopsis hederacea reddened by 

 exposure to light; of Rumex crispus and Oenothera LamarcJciana by 

 attacks of parasites ; of Spiraea prunifolia and Mahonia aquifolium 

 by decortication ; of Rubus fruticosus with autumnal coloration ; and 

 finally of young leaves of Ailanthus glandulosa in which reddening, 

 on the contrary, was disappearing. 



From observations upon gaseous exchange in the above leaves, 

 which are exemplified in the accompanying table, Combes drew the 

 following conclusions : 



Oxygen fixed (+) or lost ( ) during one hour, consisting of half- 

 hour of day and half-hour of night. 



Red leaves Green leaves 



Ampelopsis - -0872 ... -329 



Rumex + -0963 ... -8067 



Oenothera + -2442 ... + -1622 



Spiraea + -1357 ... -3226 



Mahonia + -0829 ... -1565 



Rubus + -2011 ... -0435 



Ailanthus - 1-959 - 2-589 



