Ill THE COLOURS AND PIGMENTS OF PLANTS 6i 



chemical laboratory. It is exceedingly characteristic 

 of certain of the anthocyans, and is of much im- 

 portance in the production of the colours of flowers 

 and fruits. 



The chemistry of the anthocyans has not yet 

 been fully worked out, but it seems probable that 

 they are derivatives of tannin, probably oxidation 

 products. The colouring-matters of the different 

 varieties of grapes, as well as of the leaves of the 

 vines bearing them, are said to be due to oxidation 

 products of the tannic acids which are so abundant 

 in these plants, and these colouring-matters are 

 undoubtedly of anthocyan nature. There is also 

 other evidence pointing in the same direction. 

 Tannin is probably a substance of no further use to 

 the plant, and therefore it is probable that the 

 anthocyan pigments come into the group of waste 

 products. We say probable only because, while 

 plant physiology is so imperfectly known as at 

 present, it seems hardly justifiable to apply to plants 

 terms which in relation to animals have a perfectly 

 definite meaning. 



As to the proximate importance of anthocyan to 

 the plant, there are endless suggestions and hypo- 

 theses. Into all these we cannot enter here, but as 

 a type may take a recent interesting paper by 

 Professor Stahl on the meaning of anthocyan in 

 brightly coloured foliage leaves. 



Stahl studied the bright colours of the leaves of 

 certain tropical plants, and decided that these could 

 not be regarded as warning colours — a conclusion 

 which is probably well founded ! He therefore set 

 himself to discover some physiological function. He 



