472 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



generally the case ; if neutral, the colour is blue. Anthocyan, in fact, 

 behaves towards acids and alkalis like litmus, and no doubt for the same 

 reason. Protoplasm appears to be always alkaline in reaction, and when 

 an anthocyan-containing cell is killed the pigment stains the protoplasm 

 of the cell blue. This is especially the case if tannins be present, for 

 then the dead protoplasm is tanned, and this makes it specially con- 

 ditioned to absorb pigment.* There is a general impression that the sap 

 of a cell containing blue anthocyan must have an alkaline reaction. 

 Detmer t says, concerning the blue pigment in the cell sap of the corolla 

 of Myo&otis, that the reaction of the cell sap here is slightly alkaline, for 

 the pigment becomes red by the addition of acid. And Pfeffer t makes 

 the cautious statement that the blue coloration of the Hyacinth, Blue- 

 bell, or Cranberry shows that the cell sap is neutral, or slightly alkaline. 

 I have not found an alkaline reaction in the cell sap of any flower, 

 although I have found acid and neutral sap, nor do I find any record 

 of an alkaline reaction ever having been specifically detected. So that 

 there is no reason, so far as I know, for assuming that the sap of a cell 

 in which there is blue anthocyan is other than neutral. In some plants, 

 notably among the Boraginaccce, the flower when first opened is red, and 

 then the cell- sap is certainly acid. It shortly, however, becomes blue, 

 showing that the acidity has disappeared. The blue variety of the 

 common Primrose is not a variety containing a pigment different from 

 the red anthocyan of the plants from which it was obtained. It is 

 merely a variety with less acid in its cell-sap. The blue colour is only 

 an accident 



Not infrequently cells are so gorged with anthocyan that some of it 

 separates out in the solid state, and this leads to much greater light 

 absorption, and therefore to lessened luminosity. This is the case in 

 Delphinium Ajacis, the cells of which contain needle-like crystals of the 

 blue pigment, some of the cells of the petals of AnagalUs arvensis, 

 Delphinium Comolida, Delphinium formosum, and others. The black 

 marks on the skin of the Scarlet Eunner Bean are due to solid blue 

 pigment in the epidermal cells. In cases where cells containing red 

 dissolved anthocyan deposit solid blue particles, as in the epidermal cells 

 at the base of the petals of Papaver Bhoeas, and in certain cells of the 

 petals of Cytisus Labimmm, the latter probably consist of a compound 

 of anthocyan with a proteid substance, or perhaps a tannin. The solid 

 particles are reddened and dissolved by acids, but they do not dissolve in 

 water. 



Little or nothing is known as to the chemical nature of anthocyan. 

 Pfeffer is of opinion that it is a tannin or a compound allied to the Phenols. 

 Wigand has shown that red sap is peculiarly characteristic of tannin- 

 containing plants, and that the pigment arises from a substance giving 

 tannin reactions. Pick describes a large number of cases of developing 

 shoots whose cells, which a little later are filled with red cell-sap, 

 abound in a tannin-reacting substance, the disappearance of which is 

 followed pari passu by the advent of the red pigment.§ The presence of 



* Gardiner, Proc. Camb. Phil. Soc. 1883, p. 388. 



t Detmer, Physiologic YCgttale (French translation), p. 259. 



X Pfeffer, I.e. I. p. 41)0. 



Quoted by Keeble, Science Progress, vol. i., new series, p. 406. 



