142 3Iiss Wheldale, On the nature of anthocyanin. 



(a) Those giving a greea colouration with iron salts: 

 Blue Vinca major and blue Campanula' sp., carmine pericarp 

 of Euonymus europaeus, blue Tradescantia virginiana, blue Aster 

 tripolium, blue and magenta varieties of Cineraria sp., crimson, 

 mauve, and purple varieties of autumn Chrysanthemum, crimson 

 Hieracium ruhrum, magenta variety of Helichrysum hi^acteatum, 

 pink and scarlet varieties of Zinnia elegans, mauve Auhrietia 

 graeca, brown Cheiranthus Cheiri, pink Epacris pulchella, carmine 

 Salvia didcis, purple Salvia Horminum, purplish-red Salvia 

 involucrata, blue Anemone coronaria, carmine Tropaeolum speci- 

 osum, purple varieties of Viola tricolor. 



(h) Those giving a blue colouration with iron salts : 

 Orange Alstroemeria aurantiaca, magenta Impatiens episcopi, 

 crimson Helianthemu7n vulgare, pink Echeveria retusa, magenta 

 Azalea amoena, floral bracts of Euphorbia splendens, carmine 

 leaf bracts of Euphorbia pulcherr^ima, crimson Goronilla viminalis, 

 orange Lilium Tigrinum, crimson Abutilon striatum, purple 

 Fuchsia sp., black berries of Rosa pimpinellifolia, black berries 

 of Atropa Belladonna, magenta Petunia violacea. 



From the above classification we may conclude that among 

 herbaceous plants aromatic substances giving an iron-greening 

 reaction are common. An iron-blueing reaction however is rare 

 when anthocyanin is absent, but more common when this pigment 

 is present, though it is probable that the reaction in the latter 

 case does not indicate a true tannin nature for this substance. 



When a species is in type anthocyanic with an albino variety 

 (as regards this pigment), for example Chrysanthemum, Viola, 

 Abutilon, Helianthemum, Zinnia and Helichrysum, then with 

 alkalis the albino extract is coloured yellow and that of the 

 anthocyanic type blue with a small amount of alkali but green 

 with excess. Similarly the albino extract gives a yellow precipitate 

 with basic lead acetate, and that of the type a green precipitate. 

 The iron reaction is usually the same for both type and variety, 

 though in the case of Helianthemum and Abutilon, the iron 

 reaction is green for the non-anthocyanic varieties but blue for 

 the anthocyanic type. 



A possible explanation for the reactions observed might be 

 as follows: — That many plants free from anthocyanin, and also 

 albino varieties of anthocyanic types, contain colourless aromatic 

 chromogens, probably often in combination with sugars as 

 glucosides as suggested by Overton^". These chromogens appear 

 to have acid properties and usually give an iron-greening reaction ; 

 as present in the plant in the undissociated state they are almost 

 colourless, but on addition of strong alkali a dissociable salt is 

 formed, of which the anion is bright yellow. The yellow colour 

 disappears again on neutralisation with acid, so that the reaction 



