in] OF ANTHOCYANINS 35 



case Gertz supposes that the precipitated substances are changed by 

 the reagent, or are insoluble in the new medium, and so remain. As 

 already stated, the above examples are artificial, but Gertz suggests 

 that in a similar way in the normal cell, substances may be precipitated 

 and absorb anthocyanin. This precipitation may be brought about 

 by increased concentration, or by lowering of temperature. The latter 

 was found by Molisch to be the cause of crystallisation of anthocyanin 

 in Brassica. 



As to the chemical nature of the substances which absorb antho- 

 cyanin in the cell, according to Gertz, little can be said. Often they 

 appear to be tannin-like compounds, impregnated with anthocyanin, 

 in the form of solid bodies (in young leaves of Juglans, Quercus, Rubus, 

 Ribes and others), or globules as described in the Bromeliaceae (Wallin, 

 101), Cissus (D'Arbaumont 1 ), Euphorbia (Gaucher 2 ) and Dicentra 

 (Zopf, 48). Possibly in some other cases the ground substance is 

 protein; coloured aleurone grains have been recorded by Hartig (87), 

 which are red in Laurus nobilis and blue in Cheiranthus annum, and 

 blue grains have been noted by Spiess (103) in Zea. There is also the 

 possibility, even when the anthocyanin deposits are crystalline, of the 

 stroma being of some other substance. Nageli (90) has suggested that 

 coloured protein crystalloids occur in Solanum americanum. 



We may next consider the distribution of anthocyanins in the tissues 

 of leaves, stems, flowers, fruits and seeds. 



As regards leaves, reference may be made to the work of Morren 

 (26), Pick (391), Hassack (393), Engelmann (394), Stahl (62, 405), 

 Berthold (64), Griffon (331), and Buscalioni & Pollacci (17). No very 

 general statement can be made about the histological distribution in 

 leaves beyond that the pigment is often present in the epidermis, quite 

 frequently in the subepidermal tissues also, and in many cases in the 

 more internal tissues as well. Neither can it be predicted with certainty 

 for any plant where the localisation will be, and it may vary considerably 

 in the same plant according to whether we select for investigation leaves 

 in the young, autumnal or winter condition, or leaves during the normal 

 vegetative period; or again leaves under the influence of attacks of 

 insects or Fungi. Accounts of the histological distribution in leaves 

 have been made by various authors (Hassack, Engelmann, Pick, Stahl, 



1 D'Arbaumont, 'La tige des Ampelidees,' Ann. sci. nat. (Bot.), Paris, 1881, ser. 6, 

 xi, pp. 186-253 (pp. 241, 242). 



2 Gaucher, L., 'Rechercb.es anatomiques sur les Euphorbiacees,' Ann. sci. nat. (Bot.), 

 Paris, 1902, ser. 8, xv, pp. 161-309 (p. 179). 



32 



