vi] INFLUENCING THE FORMATION OF ANTHOCYANINS 101 



a result, if it were possible, would give an even more important proof 

 that anthocyanin production is independent of chloroplastid activity. 

 A striking observation in this connection has been made by Goiran 

 (310) on Cyclamen persicum giganteum of which the flower is white 

 except for a patch of red anthocyanin at the base of the petal. Goiran 

 made transverse cuts through part of the petal, and though the petal 

 tips remained fresh, after a time they developed red pigment. This 

 result is akin to the formation of anthocyanin in leaves when the 

 conducting system is injured by cutting, or by insects, Fungi, etc. 

 There is also an observation by Gertz on white petals of Saxifraga 

 in which anthocyanin appeared as a result of insect attacks. Gertz, 

 however, failed to get any result from sugar cultures of Bellis perennis, 

 Anemone japonica, Magnolia acuminata, Tropaeolum majus, Deutzia 

 gracilis, Begonia sp., and Pisum sativum. But eventually a positive 

 result w T as obtained with white petals of Viburnum Opulus (the cultivated 

 form with neuter flowers). These petals in sugar solution formed 

 anthocyanin in either one or both epidermal layers. Thus Overton's 

 prophecy that petals might be found which would redden in sugar 

 culture appears to be justified in this case. 



It is not an easy task to set forth any general explanation of all 

 the facts recorded in the previous sections, but a short review, as far 

 as possible, of the situation may be useful at this stage. Thus, we 

 may say that two points emerge from the preceding considerations : 

 (1) that the chromogen for anthocyanin is formed in the leaf; (2) that 

 an accumulation of carbohydrates (sugars) and glucosides (including 

 the glucoside of the chromogen) leads to the formation of anthocyanin. 



One explanation offered for the reddening phenomenon has been 

 advanced by various authors, Palladin (203), Mirande (365) and Combes 

 (379), that presence of excess of carbohydrates increases oxidation 

 processes, and hence, if anthocyanin is an oxidation product, the forma- 

 tion of this pigment. Such an explanation would meet practically 

 all cases of anthocyanin formation, but there is no special evidence for 

 its justification. 



Another suggestion is that made by the author (226) ; it is based 

 on certain reversible reactions involving pigment, chromogen, glucosides 

 and sugars, and will be considered in detail in the next chapter. For 

 the moment we need only say that the hypothesis assumes that the 

 chromogen is formed from sugars in the leaf, and that increase in amount 

 of sugar leads to increased formation of chromogen with the resultant 

 production of anthocyanin, unless the chromogen be removed. 



