Colours and Pigments of Flowers, etc. 



45 



B. Pigments associated with specialised protoplasmic bodies — chromo- 

 plastids — the colour in this case being usually yellow, orange-yellow, orange, 

 or orange-red. Insolubility in water appears to be a constant characteristic 

 of this group. Two well-kuown pigments are included here : — 



(1) Carotin — a hydrocarbon of definite and characteristic properties. 

 According to Zimmermann (13), it is insoluble in water, almost so in 

 alcohol, slightly soluble in ether, more readily in benzine, and most so in 

 chloroform and carbon bisulphide. It occurs naturally and can be obtained 

 artificially in crystalline form, and is microchemically recognised by certain 

 reagents ; with concentrated sulphuric acid it gives an indigo-blue colour, 

 at first momentarily violet, and with iodine a green or greenish-blue colour. 



(2) Xanthin — again, according to Zimmermann (13), occurs in the plastid 

 in amorphous form. It is insoluble in water, somewhat soluble in ethei', 

 chloroform, and benzine, but more so in alcohol. Microchemically xanthin 

 can be recognised by giving with concentrated sulphuric acid a blue colour, 

 at first momentarily green, and with iodine a green colour. 



In addition to the above, there appear to be other plastic pigments, which 

 do not give a blue colour with sulphuric acid, but a yellow or brown. 



Antliocyanin. 



Classification of the soluble red-purple-blue pigments has always been 

 a difficult problem, but there seems to be evidence that anthocyanin is 

 a general term,, including several different pigments. The differentiation 

 made here is based on the inheritance of colour in certain genera, on the 

 sequence of flower-colour in cultivated varieties, and finally on the behaviour 

 of red pigments towards chemical reagents. 



There are present in most plants colourless or pale yellow substances, 

 soluble in water, but insoluble in ether ; with strong acids and alkalis they 

 give a canary-yellow colour, and a similar coloration or most frequently 

 a precipitate of the same colour with basic lead acetate. In some cases, 

 Eschscholtzia calif omica (Courchet(3) ), Argemone grandiflora, and yellow 

 species of Viola, these substances crystallise from extract solutions in 

 needle-shaped crystals aggregated in clusters or spherules ; solutions of the 

 crystals from the above genera reduced Fehling's solution slightly, but after 

 prolonged boiling with dilute acid, a deep yellow substance, together with 

 a reduction of Fehling's solution, was obtained, suggesting the glucoside 

 nature of the crystalline bodies. A similar glucoside is probably present in 

 Narcissus Tazetta (Bidgood (2) ). 



The colour reaction with alkalis and acids is most obvious in parts free 



