1903.] Group of Yellow Colouring Matters. 167 



L. xanthophyll. Calceolaria, Nasturtium (Tropodum). 



B. xanthophyll. Doronicum (two species), Chrysanthemum, 



Charlock (Raphanus raphanistrum), Butter- 

 cup (Ranunculus acer), Sunflower (Helianthus 

 annuus), Dandelion (Taraxacum officinale), 

 Musk (Mimulus moschatus), Laburnum 

 (Cytisus laburnum), Coltsfoot (Tussilago 

 farfara), Marigold (Calenduki qfficinalis). 



L. and B. xanthophyll. Wallflower (Cheiranthus cheiri). 



Y. xanthophyll. Tulip, Pansy (Viola tricolor}, Gorse (Ulex 



europceus). 



L. Y. xanthophyll. African Marigold (Tagetes erecta), Daffodil 



(Narcissus pseudo-narcissus). 



Thus, in the above flowers the B. xanthophyll greatly preponderates. 

 In certain varieties of the above, as the dark-coloured calceolaria and 

 wallflower and the various shades of nasturtiums and the red tulip, 

 the xanthophyll is present as usual but is masked by the presence of 

 these additional pigments, which in each case can be removed by 

 extracting with hot water in which they are easily soluble. The depth 

 of colour of the flowers appears to depend upon the amount of pigment 

 present and not upon the particular xanthophyll ; thus in the case of 

 the chrysanthemum three different varieties were examined, a very 

 rich yellow, a medium coloured and a very pale one, but in each the 

 pigment consisted of B. xanthophyll. Of the African marigold, three 

 shades of flowers were also examined, varying from a rich orange to 

 a very pale yellow, but the majority of the pigment in each consisted 

 of L. xanthophyll. 



The spectra of these three xanthophylls each consist of three bands 

 situated between the solar lines F and H, and compared to chrysophyll 

 and to one another the bands exhibit a gradual shifting towards the 

 violet, those of chrysophyll being the least refrangible and those of 

 Y. xanthophyll the most (Plate 6, figs. 1 5). They form a very 

 similar and closely connected series of spectra, which points to a close 

 relationship between these colouring matters. There is generally an 

 indication in each of a fourth more refrangible band, but this is not 

 apparent in the fresh extracts and I believe is due to spontaneous 

 change which takes place after a time. The photographic plates of 

 their spectra, as well as of chrysophyll, show that the ultra-violet rays 

 are transmitted to a considerable extent, though this visibility is some- 

 what lost in the reproduction. Though the bands of each occupy 

 different positions in the spectrum, it is by the change brought about 

 in their spectra by the action of acid that these three xanthophylls can 

 be definitely distinguished from one another. In the case of L. xan- 

 thophyll HC1 has no immediate effect, the bands fading after a time 



