1 1 8 Prof. Keeble, Dr. Armstrong, and Mr. Jones. 



We have obtained by the means described already red pigments from the 

 yellow and colourless flowers of many other plants, e.g., yellow daffodil, 

 yellow crocus, cream polyanthus, and Chinese primrose. As a rule the colour 

 is located at first especially in the veins, but it appears subsequently in the 

 whole petal. The case of the daffodil is of particular interest, inasmuch as 

 plant breeders have been at work for many years endeavouring to produce 

 a red daffodil. This work has met already with some considerable success, 

 and it may be predicted on biochemical grounds that the object will be 

 achieved completely in the near future. 



In the case of some flowers, e.g., polyanthus, reduction by means of zinc 

 dust is not necessary, the red coloration appearing after heating with acid 

 and subsequent oxidation. 



We have used the same reagents with the flowers of dominant and recessive 

 white Primula sinensis, and find that, as is to be expected on theoretical 

 grounds, dominant whites yield the red colour, and recessive whites, if they 

 yield it at all, do so to an extremely slight extent. Thus we have biochemical 

 evidence supplementary to that derived from plant-breeding experiments 

 that dominant whites possess and recessive whites lack the prochromogen 

 from which anthocyan pigments are derived. 



We have described already (Part IV) the recovery of colour which takes 

 place when a decolorised petal of the stock (Matthiola incana) is immersed 

 in water, and we have stated our reasons for regarding the recovery of 

 natural colour as the result of a process of oxidation. Subsequent experi- 

 ments confirm this view. 



Thus, by treating an aqueous solution of the purple pigment of stocks 

 with zinc dust and acetic acid in the cold, the pigment becomes first pink, 

 and is reduced subsequently to a colourless state. The colour returns 

 rapidly on exposure to air, and still more quickly when the solution is 

 warmed or treated with a drop of hydrogen peroxide. In each case the 

 original purple is recovered. If zinc dust and ammonium chloride be used, 

 reduction to a colourless state also takes place, but subsequent oxidation 

 leads to the formation of first a pale green and then a blue colour. 



Section 2. — The Formation of Pigment-producing Substances from Glucosides. 



The present state of our knowledge does not allow of a perfectly satis- 

 factory classification of the pigments which commonly occur in the flowers of 

 plants. Nevertheless, these pigments may be grouped provisionally according 

 to their mode of origin and chemical composition. 



Classified according to their modes of origin, the flower pigments fall into 

 two groups, those which are derived from the plastids, and those which are 



