CHAPTER VI 



PHYSIOLOGICAL CONDITIONS AND FACTORS INFLUENCING 

 THE FORMATION OF ANTHOCYANINS 



Connection with photosynthesis. 



An examination of the relative distribution of anthocyanin and 

 chlorophyll at once suggests that these pigments are more or less 

 complementary as regards their appearance in the plant tissues. In 

 leaves, the chief seat of chlorophyll, anthocyanin is found to a less extent 

 than in any other organ, and under normal circumstances the develop- 

 ment is most frequently confined to the epidermis (see p. 37), or to 

 a few sub-epidermal layers, often only where they overlie the midrib 

 or main veins. Moreover, when red pigment is present in the epidermis, 

 the guard cells of the stomata,. which contain chlorophyll, are generally 

 free from pigment. In petioles and stems also, anthocyanin is on the 

 whole limited to the epidermis, or to a few sub-epidermal layers. Bracts 

 of all kinds, on both the inflorescence and other parts of the plant, 

 frequently contain anthocyanin and correspondingly little chlorophyll ; 

 although flowers in the bud stage and unripe fruits have fairly abundant 

 chlorophyll, as the flowers and fruits mature the chlorophyll disappears 

 and anthocyanin develops. 



Since chloroplasts are invariably concerned with photosynthesis, 

 one would naturally conclude that the latter process and the formation 

 of anthocyanin are to some extent mutually exclusive. The existence 

 of some such alternation is further emphasised by the appearance of 

 anthocyanin which accompanies lessened photosynthetic activity, as 

 in plants towards the end of their vegetative season, in autumnal 

 reddening, in leaves in an unhealthy condition and in evergreens during 

 winter. Since all metabolic activity ultimately depends on photo- 

 synthesis, it is not a convincing argument that a decline in general 

 metabolism (apart from photosynthesis) may directly bring about 

 the formation of pigment. There is without doubt good evidence for 



w. p. 6 



