84 PHYSIOLOGICAL CONDITIONS AND FACTORS [CH. 



The more intimate connection between anthocyanin and sugars will 

 be discussed in a later chapter. 



The experiments of decortication, etc., lead also to the conclusion 

 that the chromogen 1 of anthocyanin is synthesised in the leaves. For 

 in cases where leaves and shoots have reddened owing to the blocking 

 of the translocation current, less development of pigment has often been 

 noticed in flowers and fruits. Gautier (175) made various experiments 

 on vines in order to illustrate his view that the chromogen of the grape 

 pigment is synthesised in the leaves, and is oxidised after passing into 

 the fruit. Vine branches were deprived of their leaves, and this was 

 shown to prevent a development of pigment in the fruit. In another 

 experiment, the petioles of the leaves were ligatured with the result 

 that the fruits remained green and the leaves themselves reddened. 

 Ravaz (380), on the other hand, grafted a vine with purple grapes on 

 to a white-fruited variety, and found that although the white variety 

 produced no pigment in the leaves, the fruit of the graft was coloured 

 every year. Hence Ravaz concludes that the pigment is synthesised 

 in the fruit itself, though the latter may be nourished by the leaves. 

 A direct connection between leaves and flower-colour may be demon- 

 strated by removing a developing inflorescence from a plant, such as 

 Digitalis purpurea, when the leaves will generally turn red. Gertz (19) 

 observed the same result in a plant of Geum rivale from which the flowers 

 had been cut off. 



There is also reason to believe that special richness in nutriment, 

 or synthetic products, is connected with anthocyanin formation. An 

 experiment is quoted by Berthold as illustrating this point. From 

 two- or three-year old individuals of Acer pseudoplatanus all buds were 

 removed but the terminal one, which, as a result, received an excessive 

 amount of nutriment and on development was strongly reddened. 

 Some such explanation, as Gertz suggests, may account for the excessive 

 reddening of leaves of adventitious shoots arising at the base of felled 

 trees (Populus, Tilia, Acer). 



Bonnier (294, 307, 328) and Heckel (300) have noted that a greater 

 intensity of flower-colour is produced in many species when grown at 

 high altitudes, as compared with the colour of the flowers in lowland 

 regions. It is conceivable that this increase in intensity of colour 



1 The chromogen, as we shall see later (p. 109), is in all probability a flavone occurring 

 in the form of a glucoside. There is reason to believe that, not only does the synthesis 

 of glucoside from flavone and sugar take place in the leaf, but also the synthesis of the 

 flavone itself from sugars. 



