66 Various Tints of Autumnal Foliage. [January, 



are insoluble in water, but soluble in alcohol or bisulphide 

 of carbon ; the spectra have all a very well-marked ab- 

 sorption-band in the red, but the green more or less com- 

 pletely transmitted, so that the prevailing tint is a more 

 or less modified green. 



The second class of colouring matters may be described as 

 the xanthophyll group. These are characterised by being in- 

 soluble in water, but soluble in alcohol and in bisulphide of 

 carbon ; the spectra show absorption at the blue end, often 

 with more or less well marked narrow bands, but the red, 

 yellow, and yellow-green are freely transmitted, so that the 

 general colour is clear yellow or orange. The different 

 species are distinguished by the character and position of 

 the absorption-bands, which are best seen when the colour 

 is dissolved in bisulphide of carbon. A considerable number 

 are found in various fruits, flowers, and roots, but only two 

 are so commonly met with in leaves as to claim attention in 

 this paper. These appear to be the same as the two which 

 give rise to the difference in the colour of the yellow interior 

 and the orange exterior of some carrots. They may be ob- 

 tained by dissolving in hot alcohol, and agitating the cold 

 solution with excess of bisulphide of carbon, which subsides 

 to the bottom with more or less of the colour, and leaves in 

 the alcohol all other substances soluble in water. Both give 

 spectra with two rather obscure absorption-bands, which lie 

 further from the blue end in the case of colour from the 

 external layer of the carrot, and the colour of this is orange, 

 and of the other yellow. This latter is the kind most com- 

 monly met with in yellow leaves, from which it may be ob- 

 tained in the manner just described, and when nearly pure 

 it is of the same tint as gamboge. The orange colour is 

 more rare, but occurs in leaves fading to a deeper and more 

 orange-yellow, as, for instance, in those of the India-rubber 

 tree, to which it gives a tint closely corresponding to that of 

 Indian-yellow. It also occurs in a more pure state in the 

 ripe envelope of the fruit of the common winter cherry 

 {Physalis Alkikengi), to which it gives a still more orange- 

 coloured tint, approximating to that of the exterior layer of 

 the carrot. There may be some other colours besides these 

 having bands in intermediate situations, but, on the whole, I am 

 disposed to regard them as variable mixtures of the twojust 

 described. 



Since the name of erythrophyll has been already applied 

 to the red colour of leaves in autumn, it will be best 

 to adopt it as that of a group containing a number of 

 different species. These may be said to be characterised by 



