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JOURNAL OF THE KOYAL HORTICULTURAL SOCIETY. 



2. Soluble Floral Pigments. 



This group may be divided into two sub-classes, namely : — 



(a) The pigment or pigments which are in colour red or blue, or some 

 combination of red or blue, such as purple, crimson, lilac, heliotrope, 

 violet, &c. This is the anthocyan of Ch. Maquart. It constitutes the 

 Cyanic series of A. P. de Candolle. 



(b) The pigments which, being soluble in the cell-sap of plants, colour 

 the sap yellow, orange-yellow, orange, or orange-red. There are certainly 

 several of these pigments, and they may be said to constitute a Xanthe'ic 

 scries of pigments. 



The Cyanic Series, or Anthocyan. 



Anthocyan was the name applied by Maquart * so long ago as 1835 to 

 that pigment which becomes red by the action of acids, and blue again 

 by the action of alkalis. In flowers it is almost entirely confined to the 

 epidermal cells ; where it is found in leaves and other organs, it is 

 situated, as often as not, in deeper lying tissues. 



There has been in the past a considerable difference of opinion as to 

 whether the substances of various colours, which are classed together as 

 anthocyan, are a single pigment whose colour depends on the acidity, 

 neutrality, or alkalinity of the cell- sap, or whether there is a number of 

 such pigments. A. Hansen distinguished between the colouring matter 

 which gives red tints and those giving blue and violet tints. N. J. C. 

 M iiller t was of opinion that there is a great variety, but he gives no 

 evidence that he experimented with pure pigments. On the other hand, 

 Krukenberg % regards them as identical. The fact is that there is no 

 certainty, and not even a strong probability, that the pigment has been 

 ever obtained completely separated from other substances, and until that 

 has been done nothing certain can be said about it. Since it has not yet 

 been proved that there is more than one cyanic pigment, there is no need 

 to consider it as other than a single substance, especially as we have a 

 colouring matter in litmus, whose composition is known, which also 

 becomes red on treatment with acid, and blue again on treatment with 

 alkalis. 



There is no question about the red reaction of anthocyan with acids, 

 but it is generally stated that under the action of weak alkalis it becomes 

 blue, and of stronger alkalis first blue, then green, and then yellow. For 

 example, Van Tieghem § says : " Some cell-sap holds in solution various 

 nitrogenous colouring matters. The commonest is anthocyan. The 

 aqueous extract of Viola, for example, becomes bright red with acid ; 

 cautiously neutralised it is blue; excess of alkali makes it green." Zini- 

 mermann " says that the solution of anthocyan in water has, according 

 as its reaction is more or less acid or alkaline, a red, violet, blue, blue- 



* Ch. Maquart, Die Farben der Blilthen, Bonn, 1835. 

 f N. J. C. Mfiller, JahrbiicJi filr jciss. Bot. xx. 1889. 



X Krukenberg, Grundziige eincr vergleichende PJujsiologie der Farbstoffc und der 

 Farben, p. 116. 



§ Von Tieghem, Traiude Botamgue, p. 535. 

 || Ziinraerniann, I.e. p. 107. 



