92 PHYSIOLOGICAL CONDITIONS AND FACTORS [CH. 



The appearance of anthocyanin is accompanied by an accumulation 

 of oxygen in the tissues ; the disappearance of the pigment is, on the 

 contrary, accompanied by a considerable loss of oxygen. The variations 

 detected in the gaseous exchange during the formation of red pigment 

 are concerned with assimilation ; it therefore appears that the produc- 

 tion of these pigments is intimately bound up with the phenomenon 

 of assimilation. This accumulation of oxygen on anthocyanin formation 

 can be explained by the diminution in intensity of assimilation, and 

 'in the modification produced in the ratio of gaseous exchange in assimi- 

 lation. Further, the accumulation in the cells of soluble carbohydrates 

 which accompanies anthocyanin production accelerates oxidation, and 

 the gaseous exchange is fundamentally modified. 



Effect of drought. 



Here again the direct effect is difficult to estimate owing to the 

 simultaneous effect on photosynthesis, but whether direct or indirect, 

 there is ample evidence that drought increases anthocyanin formation. 

 Molisch (316) found that leaves of Peireskia aculeata, Tradescantia, 

 Panicum, variegatum and Fuchsia reddened strongly if only watered a 

 little. The author has made the same observations for pot plants of 

 Pelargonium. Eberhardt (347) also found an increase of anthocyanin 

 in leaves of Coleus Blumei and Achyranthes angustifolia when grown 

 in a very dry atmosphere. According to Warming (327, 346) plants 

 such as Tillaea aquatica, Peplis Portula and Elatine are green when 

 growing in water, though individuals on land may be strongly red. 



The physiological drought of salt marshes may similarly explain 

 the development of anthocyanin in halophytes (Salicornia, Suaeda). 



An interesting case of the connection between reddening and drought 

 has been observed by Miyoshi (375). This author noticed that the 

 leaves of certain tropical trees, especially Terminalia Cattapa, in the 

 East Indies, Ceylon and Java, take on a beautiful red colour before the 

 leaf-fall. The reddening is described as affecting at first a few leaves 

 only, but later the number increases. Of the early stages the author 

 says: "Vor der Feme betrachtet erschienen die gefarbten Blatter wie 

 rote Bliiten in voller Pracht." Since the phenomenon takes place at 

 the dry period of the year, Miyoshi suggests the term 'Trockenrote,' 

 and considers the causes of reddening to be drought coupled with strong 

 insolation. 



