FLORAL COLOURS AND PIGMENTS. 



477 



the hydrolysis of glucosides which exist dissolved in the cell-sap of the 

 plant. From the petals of the yellow Wallflower — which, however, owes 

 its colour wholly or mainly to chromoplastids — Perkin obtained, by the 

 decomposition of a glucoside, the yellow colouring matters quercetin and 

 isorhamnetin. From white Hawthorn blossoms he obtained quercetin ; 

 from the yellow flowers of Delphinium Zalil he got the same colouring 

 matters as from the Wallflowers ; from the flowers of Gossypium 

 herbaceum a yellow colouring matter called gossypetin ; and compounds 

 of the same class have been obtained from flowers of Delphinium Con- 

 solida, Batea frondosa, Bobinia Pseud- acacia, and others. In all these 

 cases the colouring matter exists in the flowers in the form of glucosides 

 which are colourless or only slightly coloured. They are hydrolysed by 

 dilute mineral acids with the production of a reducing sugar and the 

 colouring matter. It is known, however, that many glucosides are decom- 

 posed by ferments existing in plants. Glucosides are so frequently to be 

 found in floral segments as to be almost universal, and it does not seem 

 unreasonable to suggest that it may yet be shown that many other of the 

 xantheic pigments are glucosides, or the products of the decomposition of 

 such compounds. 



It is worthy of note that when, within the limits of a single species, 

 red or blue, yellow and white varieties are known, the yellow pigment is 

 always xantheic, according to the varieties I have been able to examine. 

 Indeed, so often does anthocyan disappear and a dissolved yellow pigment 

 appear in its place that there is probably a close connection between 

 them. Carnations, Iceland Poppies, Antirrhinums, Hollyhocks, Lupins, 

 Primroses, Stocks, and Hyacinths have already been mentioned. Roses 

 and Dahlias, although hybrids of many species, have, I think, no yellow 

 ancestors other than those whose pigment is xantheic. The common 

 Primrose and the Hyacinth are most remarkable in that they exhibit blue, 

 red — and every hue formed by the admixture of blue and red — white, and 

 yellow varieties, the central yellow xantheic pigment of the Primrose being, 

 however, always present. The experience of the selector is, I believe, that 

 the yellow variety is the last to arrive ; so that the course of colour 

 variation in flowers is from red or blue to albinism, and then from the 

 white form to the yellow. 



If this variation course hold good for all, then xantheic-coloured 

 flowers may be placed at the extreme limit of colour variation, and, for 

 example, the universal yellow Primrose is a colour variety of a red or 

 blue-coloured type. But it is well known that many such yellow-flowered 

 plants develop anthocyan in some individuals. This may be looked upon 

 by some as cases of regression or atavism, and the modern blue Primrose 

 may be regarded as a reversion to a blue ancestor, or, at any rate, an 

 anthocyan-containing ancestor. But it is as well to remember, as de Vries 

 has pointed out, that individuals amongst most species of plants are 

 subject to the production of anthocyan in their organs, and in such cases 

 the colour is not a character belonging to any single organ or cell, nor is 

 it bound to a morphological unit. It is a free physiological quality, not 

 localised, but belonging to the whole plant.* Although this is true of the 

 red and blue Primrose, that anthocyan is produced to a greater or less 



* De Vries, I.e. p. 144. 



