FLORAL COLOURS AND PIGMENTS. 



473 



sugar seems to have some effect. Ewart observed that immersion in 

 sugar solution may induce a formation of red pigment in cells of certain 

 aquatic plants, and Overton confirmed this observation.* 



The immediate precursor of anthocyan in plant tissues is most 

 probably a soluble colourless compound. It frequently happens that the 

 colourless sap of the cells of flowers takes a bright red colour with an 

 acid, the red colour being converted to a blue one by the subsequent use 

 of an alkali. I find such colourless cells near others containing 

 anthocyan, in some albino varieties which normally would contain 

 anthocyan, and in the colourless unopened buds of some flowers which 

 later would contain anthocyan. 



In most cases, although not in all, light is necessary for the develop- 

 ment of the anthocyan pigment. Many flowers do not develop any 

 colour in darkness, nor do many fruits, such as Apples and Pears, unless, 

 they are in strong light. On the other hand, the flowers of Tulipa 

 Gcsneriana and Pulmonaria officinalis, as well as Red Grapes, assume 

 their normal coloration in complete darkness. 



Anthocyan is inherited except in the comparatively rare cases of 

 complete albinism. On the other hand, cases are recorded where two 

 plants with white flowers have had progeny with anthocyan -pigmented 

 flowers. Bateson and Saunders describe cases of this happening with 

 species of Matthiola.t 



The Xantheic Series. 



This is at present the most suitable name for the series of pigments 

 which, being soluble in the cell-sap of flowers, colour it yellow, orange, 

 orange-red, and even a bright brick-red. When the dissolved pigment 

 is not present in strong solution it is not difficult to select on inspection 

 flowers containing one of these pigments from amongst others which owe 

 their colour to xanthin or carotin. In the former case the colour is 

 more delicate and transparent than in the latter, and it may be said 

 generally that all floral colours of a primrose or sulphur yellow are pro- 

 duced by dissolved pigments. Where, however, the colour is a stronger 

 yellow, or inclines to orange or orange-red, the microscope or reagents 

 must be used. 



Fremy and Cloez designated the soluble pigments of flowers ; which 

 become a reddish-brown with sulphuric acid, xanthein. I include all these 

 pigments, for convenience, in the xantheic series, although very few of 

 them give a red-brown colour with this reagent. 



The pigments of this series are not common in flowers ; 'yet there is a 

 fair number which owe their colours to them. It appears that all the 

 colour effects from yellow to red may be produced by one and the same 

 pigment, according to its degree of concentration in the cell-sap. 



They may be divided, probably quite artificially, into two subdivisions 

 according as sulphuric acid produces an orange or red colour with the 

 pigment, or has little or no effect upon its colour. There is no doubt 

 that here, as with anthocyan, the effects of reagents upon the pigment 

 in situ, or upon a crude extract of the tissues, are complicated by the 

 * Pfeffer, I.e. I. 496, footnote. 



f Bateson and Saunders, Royal Society, Report to tlie Evolution Committee. 



I 



