148 P. Q. KEEGAN [februauy 



on advanced oxidation evolves brown-red or muddy anhydrides more 

 than sufficient to neutralise and overcome any tendency to blue 

 coloration incident to the presence of gallic acid. 



Nevertheless, it is evident that gallic acid is not the only substance 

 that may officiate as chromogen in the outcoming of vivid and brilliant 

 blues. The genus Zinum presents a remarkable phenomenon in this 

 connection. Of some fifty species of this genus about seventeen are 

 pure blue, and the rest are either yellow or purple, lilac, crimson, rose, 

 pink, or pure white. The most astonishing species is L. grandiflorum 

 (coccincum) which is the one crimson amidst a genus predominantly 

 blue : it contains no gallotannin or gallic acid, but there is some rutin 

 and iron-greening tannin, and there is a small amount of free phloro- 

 glucin in the plant itself. Now, if ever there was a red flower which 

 is or has been naturally and originally blue it is this one, as the 

 following reactions will show. The alcoholic extract of the petals is 

 of a magenta - red colour, and the filtered aqueous extract of its 

 evaporated residue yields with acetate of lead a blue colour, and then 

 when acetic acid is added in large excess the blue colour still remains ; 

 with subacetate of lead it gives a pure blue colour ; with bicarbonate of 

 soda a grayish-blue turning grayish-green, and with oxalic acid added a 

 bright scarlet red is obtained ; with acetate of magnesium a splendid 

 green, and when acid is added the original red is restored. Thus we 

 see that in the presence of heavy bases the blue coloration persistently 

 remains even in the presence of a considerable excess of free organic acid ; 

 with light and feeble bases, on the other hand, the addition of a small 

 quantity of acid determines a distinctly red reaction. And all these 

 facts seems to me to demonstrate what I consider to be quite excep- 

 tional, viz., that in Linum coccineum the red coloration of the flowers 

 is produced by the accidental presence of free acid affecting a natur- 

 ally blue pigment. It is hardly necessary to subjoin, that in the vast 

 majority of cases, whether the flower be either red or blue, the 

 particular tint is not influenced or created by the neutral or acid 

 condition of the cell sap. 



By what circumstances, then, is the particular tint created or 

 influenced ? In order to answer the question satisfactorily two facts 

 must be minutely considered : — 1. Chemical, the presence of quercetin 

 in the form of rutin, etc, in the corolla. 2. Physiological, the posses- 

 sion by the corolla of energetic respiratory and transpiratory functions, 

 with the result that the substances contained in its cells undergo an 

 oxidation more or less vigorous and complete. In my previous paper 

 I showed that the red pigments of flowers were specifically incidental 

 to tannic chromogens which contain phloroglucin in their molecules and 

 yield phlobaphenes, i.e. a series of anhydrides, the lower of which are 

 crimson and the higher are red-brown; while the blue pigments were 

 incidental to acid tannins or to tannins which yield acids on oxidation. 

 Now, only a slight chemical experience is requisite for the under- 



