iii THE COLOURS AND PIGMENTS OF PLANTS 61 
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 
