FLORAL COLOURS AND PIGMENTS. 



169 



soluble in chloroform, forming an orange-red solution, and in carbon 

 bisulphide to a blood-red solution. As already stated, concentrated 

 sulphuric acid dissolves it to a blue solution after turning it momentarily 

 violet. Iodine in potassium iodide solution turns it green, while alkalis 

 have no effect upon its colour. 



The pigment, which, however, occurs most commonly in chronio- 

 plastids, is yellow or orange-yellow in colour, according to its concentration, 

 and has not yet been obtained in the crystalline ' form. It is soluble in 

 alcohol to a yellow solution, and on evaporation of the solvent the pigment is 

 deposited in oily globules of a yellow colour which on complete evapora- 

 tion form a greasy yellow layer. This is turned blue by concentrated 

 sulphuric acid after a momentary green ; it first becomes green, and is 

 then immediately bleached by strong nitric acid ; it becomes green by 

 solution of iodine, and it is unaffected in colour by alkalis. Its 

 reactions are therefore very similar to those of carotin. This is the 

 pigment which was named xanthin by Fremy and Cloez.* It is not by 

 any means certain that xanthin is a single or even a distinct pigment. 

 There are indications that it may be a compound of carotin, or some 

 substance allied to carotin, with a fatty body. 



Carotin and xanthin constitute the xanthic series of pigments con- 

 stituted by A. P. de Candolle in his " Physiologie Vegetale." A. Hansen f 

 called them lipochromes — colouring matters belonging to the fatty 

 group — and this name is retained by zoologists for a series of pigments, 

 red, orange, or yellow, with similar properties found in animal bodies. 



The presence of xanthic pigments in a flower may be demonstrated 

 by placing a drop of concentrated sulphuric acid on the spot to be tested. 

 If either or both be present a blue, colour will result— often, however, a 

 green, owing to the presence of another substance giving a deep yellow 

 colour with the acid. 



Since nearly all yellow flowers owe their colour to chromoplastids 

 containing xanthin, it is not necessary to furnish a list here. 



Courchet describes, in the article already referred t°, the chromo- 

 plastids of the flowers of Aloe, which contain amorphous pigment 

 granules which are neither carotin nor xanthin. The pigment dissolves in 

 alcohol to a currant-red solution which becomes rose-red on concentra- 

 tion, and on evaporation gives up red globules. These are coloured a 

 yellowish-green by concentrated sulphuric acid. 



Marshall Ward and Miss E. Dale t examined microchemically the 

 pigment from the chromoplastids of the flowers of Gastcria formosa, a 

 genus closely allied to Aloe, and found the pigment to have essentially 

 the same reactions as Courchet found for that of Aloe. 



The floral axis of Ncottia Nidus-avis contains chromoplastids which 

 enclose crystals of a brown pigment. Very little is known of this 

 pigment. 



* Fremy and Cloez, " Note sur les Matieres colorantes des Fleurs," Journal de 

 Pliarmacie, t. xxv., p. 854. 



f A. Hansen, Die Farbstoffe der Bliithen unci der Friichte, Wiirzburg, 1884. 



X On Craterostigma pumilum, Transactions of the Linn. Soc., Botany, vol. v. 

 part 10. 



