in] OF ANTHOCYANINS 39 



Chatin (28) notes that anthocyanin occurs in deep-seated tissues 

 in thicker petals, such as Ulloa and Asclepias, whereas in thinner petals 

 it is usually confined to the epidermis. 



The most interesting feature in connection with the histology of 

 coloured petals is the combination of colour effects produced by the 

 simultaneous presence of two, or even more, pigments in the cells. 

 Strictly speaking, the plastid pigments, i.e. the yellow, orange-yellow 

 and orange colouring matters which are bound up with special proto- 

 plasmic structures the plastids, have no place in this account; and 

 the same may be said for the soluble yellow pigments (mostly flavones). 

 But both these classes occur so often with anthocyanin, and so frequently 

 modify its colour, that some mention of them at this point will not be 

 out of place. References can be made, in addition, to other authors; 

 Hildebrand (30) wrote an early account of flower pigmentation, including 

 combinations of plastid and sap colours; there is also an interesting 

 paper by Bidgood (18) on flower colours, and many detailed observa- 

 tions by Dennert (14) and by the author (211). 



One of the most frequent combinations of pigments is purple, 

 purplish-red, or red anthocyanin and yellow plastids. The resultant 

 colour may be brown (Cheiranthus Cheiri, Tagetes signata), crimson 

 (Zinnia), scarlet (Geum coccineum), or orange-red (Tropaeolum majus); 

 there are of course a great many other cases of combination of these 

 two pigments, and a correspondingly large number of shades of brown, 

 crimson, or scarlet, as the case may be. A less frequent combination is 

 dark brown, brownish-black, or black resulting from purple anthocyanin 

 and chloroplastids. This effect is produced in some Cypripedium 

 flowers, and we have already noted it in the case of leaves (see p. 19). 

 The brown or black effect is due to the fact that the two pigments are 

 complementary as regards the rays they absorb ; those which are not 

 absorbed by chlorophyll are absorbed by anthocyanin, and so the 

 result is negative as regards colour. But black or brown is not always 

 due to this combination; the black spots on Adonis and Papaver 

 flowers owe their appearance to deep blue cell-sap, and in the dark 

 markings on some varieties of Bean (Phaseolus) seeds the cells contain 

 purple anthocyanin. There are, in addition, true brown and black 

 pigments which appear in some flowers as in the spots on the alae of 

 Vicia Faba 1 . 



1 Mobius, M., 'Das Anthophaei'n, der braune Bliithenfarbstoff,' Ber. D. hot. Ges., 

 Berlin, 1900, XVHI, pp. 341-347. Schlockow, A., Zur Analomie der braunen Bliiten, 

 Inaugural-Dissertation zu Heidelberg, Berlin, 1903. 



