THE OXIDASES IN RELATION TO PIGMENTATION 275 



green salts and oxidizes to a red compound which would 

 itself pass for an anthocyanin if it were not insoluble in 

 water. This oxidation is effected by plant oxidases, or 

 spontaneously in water or solutions of halogen salts. 

 Bartlett expresses the opinion that in the cell it is probable 

 that the chromogen, in the form of a glucoside, becomes 

 oxidized to an anthocyanin. 



THE ARTIFICIAL PRODUCTION OF COLOURED SUBSTANCES 

 SUPPOSED TO BE ANTHOCY ANINS . 



It has been thought by some that anthocyanins are 

 derived from tannins, and, indeed, in the writer's (1913) 

 own experience the mature leaves of Vitis Veitchii contain 

 tannin and lack anthocyanin, whereas when the autumnal 

 red anthocyanin appears in them they are free from 

 tannin. 



Wissemann (1912) has studied the distribution of tannin 

 and anthocyanin in a very great number of plants belong- 

 ing to the most diverse orders. He could not, however, 

 find any precise relation between the occurrence of the 

 two substances, but ascertained that, in a general way, 

 when they varied with the age of the plant they varied in 

 the same sense. 



However this may be, Malvezin (1908) obtained a wine- 

 red colour by heating green grapes with 2 per cent, hydro- 

 chloric acid under pressure at 120 for half an hour. Simi- 

 lar results were obtained with the tannins from hops, from 

 Prunus domestica, P. avium, Ampelopsis sp., but not with 

 those from the oak. He also records that gallotannin 

 gives a red- violet precipitate when allowed to stand in 

 sunlight with hydrochloric acid and formaldehyde. This 

 is soluble in dilute aqueous alcohol, giving a red- violet solu- 

 tion which becomes blue-green with ammonia. 



