ANTHOCYANINS 



OCCURRENCE. 



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The occurrence of a red, blue, or purple pigment, either 

 dissolved in cell sap the exact colour depending on the acid, 

 alkaline, or neutral reaction of the cell sap or, less frequently, 

 in the form of needle-shaped crystals, as in the case of Del- 

 phinium ajaciS) is a common phenomenon, and is generally 

 ascribed to the presence of the pigment anthocyanin. It is, 

 however, doubtful whether all such colorations are due to antho- 

 cyanins ; thus Molisch found that the red colour assumed by 

 the leaves of the aloe, on exposure to high insolation, is due 

 to the formation of carotin within the chloroplasts. 



The presence of anthocyanin is due to many causes, light, 

 especially when of high intensity, being important. For ex- 

 ample, apples and other fruits and also the vegetative organs 

 of certain plants will not assume a red colour if kept in 

 darkness ; on the other hand, light does not appear to be 

 of such importance in the case of the roots of the beet. 



In other instances the aerial vegetative organs of many 

 varieties of plants, e.g. certain Chenopodiaceaae, are charac- 

 terized by a red colour the presence of which is seemingly 

 independent, or nearly so, of external conditions. Thus 

 Salicornia ramosissima may be found in two forms, one apple 

 green and the other crimson, the intensity of which varies in 

 different years. In such cases there is good reason for sup- 

 posing that these colours are of an hereditary nature and 

 come true from seed. The same also appears to be true for 

 different forms of beet which are used for horticultural pur- 

 poses. On the other hand, in the familiar example of the 

 copper beech this is not so, the copper-coloured foliage, due 

 to the combined effect of a red cell sap and the green of the 

 chlorophyll, first originated, it is stated, as a sport and is 

 propagated by means of cuttings. 



Properties. 



The chief physical property of anthocyanin is its absorp- 

 tion 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. 



