244 PIGMENTS 



By microchemical methods it is possible to ascertain the 

 nature of many of these factors present in the plant, and by 

 such means Keeble and Armstrong* have established many 

 facts relating to the distribution of oxydases in Primula 

 sinensis and their relation to the formation of pigments. 



The method employed by these authors is the treatment 

 of the tissue with suitable reagents dissolved in media, termed 

 hormones, which solvents cause the plasmatic membranes to 

 become permeable to the reagents, and also renders active 

 the enzymes contained within the cell. One such substance 

 is alcohol. 



To take an example : a-naphthol is commonly used as an 

 indicator for oxidases ; treatment of the petals of Primula 

 sinensis with an alcoholic solution of a-naphthol decolorizes 

 the tissues, but on then treating the tissue with hydrogen 

 peroxide a coloration obtains, and a comparison of this pre- 

 paration with the original, indicates that the distribution of 

 the pigment in the petal coincides exactly with that of a per- 

 oxidase. In some varieties of this same plant there is no 

 need to add hydrogen peroxide, the characteristic reaction 

 being obtained by the oxydase reagent alone. 



Properties. 



The chief physical property of anthocyan is its absorption 

 spectrum. Engelmann found that it is complementary to 

 that of chlorophyll, the main absorption bands being in the 

 yellow and yellow-green, with minor ones in the blue end 

 of the spectrum. 



Questions relating to the energy relationship between this 

 and other pigments and chlorophyll are outside the scope of 

 the present consideration ; it may be mentioned, however, 

 that it has been stated that leaves containing anthocyan have 

 relatively less chlorophyll than those which have no red 

 pigment. 



With regard to the chemistry of this red colouring matter 

 little is known. According to Pick and others, it is related 

 to the tannins, for a red sap is characteristic of tannin-con- 

 taining plants, and the precipitate appearing in the palisade 



* Keeble and Armstrong : " Proc. Roy. Soc, Lond.," B., 1912, 85, 214, 460. 



