FLORAL COLOURS AND PIGMENTS. 



471 



green, green, or yellow-green colour. Newbigin • says that alkalis change 

 anthocyan from red to blue, green, and yellow successively ; an excess 

 bleaches it. And N. J. C. Muller says that solution of caustic potash on 

 various red pigments gives blue, blue-green, green, yellow, and brown 

 colours. 



This much is certain, that alkalis acting directly on the coloured plant 

 tissues, as well as when they are applied to the crude residue of an 

 alcoholic or watery extract of the tissues, nearly always show some such 

 series of colour reactions as those stated above. I will endeavour to show 

 the reasons for this presently. 



Naylor and Chappel f separated a substance from the petals of Bosa 

 gallic a which they took to be the pure red pigment of the flower. This 

 was a red amorphous substance which deepened in colour on the addition 

 of dilute sulphuric acid, but with solution of potash it gave a deep red 

 with a green fluorescence, and with an excess of potash a yellowish-brown. 

 Senier % also claimed to have isolated the anthocyan from this flower. 

 He found it to be an acid compound which formed crystalline salts with 

 the alkalis and amorphous salts with certain of the heavy metals. 



Now solution of potash does not give a deep red colour when applied 

 to the petals of Bosa gallica, but first a blue and then a green, or a green 

 at once, according as the solution of potash is weaker or stronger, and it 

 therefore appears that Naylor and Chappel were not dealing with antho- 

 cyan in their experiments, not at any rate as it exists in the flower. 



There exists in the cell-sap of most flowers a substance or substances 

 — in some cases glucosides, in others carbohydrates — which give a deep 

 golden-yellow colour with alkalis and with concentrated mineral acids. 

 The consequence is that the application of an alkali to an anthocyan- 

 containing flower very often gives a green colour due to the blue 

 colour of the alkaline anthocyan plus the yellow colour also produced at 

 the same time by the alkali with the other substance. If the reagent 

 be weak the anthocyan is first turned blue and the yellow comes later ; 

 if the alkali be strong the green colour is produced at once. Presently 

 the anthocyan is destroyed by the alkali and the yellow colour remains. 

 This may easily be tested by placing suitable flowers for a short time in 

 an atmosphere of ammonia, or in a solution of soda or potash. The gas, 

 however, acts more evenly. But there are floral tissues containing antho- 

 cyan which become only blue with alkaline solutions. The epidermis 

 and hairs of the inner surface of the labellum of Cypripcdium Spiee- 

 r la u urn contain such pigment. And there are even others which with 

 an alkali give first a green colour and then a blue. It may be laid down 

 as a general rule that the alkali test is not trustworthy when applied to 

 the tissues or the crude extracts of them, and the results ought to be 

 checked by microchemical tests and by the use of other reagents. 



The actual colour of the anthocyan in flower cells depends upon the 

 reaction of the cell- sap. If this be decidedly acid, the colour is red ; if 

 weakly acid, the colour is something between red and blue, and this is 



* Newbigin, Colours in Nature. 



f Naylor and Chappel, " Note on the Colouring Matters of Rosa gallica" Phann. 

 Journ. August 13, 1904. 



% Senier, Pharm. Journ. [3], 7, p. 650. 



