350 PIGMENTS 



quercetrin, will separate out in yellow crystals, having a deep 

 purple mother liquor which will give the reactions of antho- 

 cyanins. 



In the case of those flowers in which the anthocyanin 

 pigment predominates, such as in most of the blue, red, or 

 purple flowers, the particular shade of colour is due partly 

 to the configuration of the anthocyanin concerned and partly 

 to the reaction of the cell sap. Somewhat conflicting views 

 on this question are held by Shibata * and others. 



These facts explain the colour variations produced by the 

 same cyanidin occurring in the same or in different flowers, 

 it having been found, for example, that the same cyanidin 

 was responsible for the colour of the cornflower and of the 

 red rose.f Thus when combined, as in the case of cyanidin 

 chloride, with mineral acid or in the plant with organic acids, 

 the compound has a red tint. When treated with alkali, blue 

 metallic salts are formed, while the arrangement shown in 

 the formula IV. (p. 346) represents a neutral compound having 

 a violet tint. The neutral violet-tinted delphinin has been 

 isolated from Delphinium consolida by Willstatter and Mieg,J 

 and has been shown to turn blue with alkali, and red with 

 acids ; the colour would therefore appear to act as an indica- 

 tor in the plant itself, showing whether the cell sap is neutral, 

 acid, or alkaline. 



Willstatter § further found that the cornflower contained 

 three modifications of the same anthocyanin, namely the 

 purple form of cyanin itself, the blue form which is the sodium 

 salt of this, and the red oxonium salt of the cyanin with some 

 organic acid present in the plant. 



Sometimes it is observed that the leaves of certain plants 

 when first they unfold are bright red and that in a few days 

 this colour fades away and the green colour is seen. Noack || 

 has investigated this phenomenon in Polygonum compactum, 



* Shibata, Shibata and Kasiwagi : " J. Amer. Chem. Soc," 1919. 4'» 

 208. 



t Willstatter and Nolan : " Annalen," 1915, 408, i. 



X Willstatter and Mieg : id., igi^, 408, 61. 



§ Willstatter : id,, 1913, 401, 189. 



II Noack : " Zeitsch. Bot.," 1918, 10, 561. 



