1871-] Various Tints of Autumnal Foliage. 69 



colours which vary in tint from that of " light red " to those 

 of burnt umber and raw sienna. 



The fifth group of colours consists for the most part of 

 various browns, and therefore I propose to distinguish it by 

 the term phaiophyll group. In most cases they are due to 

 the oxidisation of chrysophyll or other previously-existing 

 soluble compounds, as may be proved artificially. There 

 must be, at all events, several colours of this group, but their 

 accurate determination is difficult, because they do not give 

 well-defined absorption-bands. On the whole they may be 

 said to be soluble in water and not in bisulphide of carbon, 

 but in some cases water alone dissolves them very 

 sparingly, and they are more soluble in dilute alcohol, 

 along with an acid. 



When leaves pass into complete decay they turn dark 

 brown, and ultimately become nearly black. This is 

 evidently due to the formation of dark coloured substances 

 allied to humus, but their accurate determination would be 

 very difficult, and I have not yet studied them very much. 

 Though it may be convenient for our present purpose 

 to separate these more or less black colours from the 

 brighter browns of the phaiophyll group, yet I am by no 

 means convinced that there is any actual distinction between 

 them. They are no doubt produced by the decomposition 

 of most varied compounds, both soluble and insoluble ; and 

 since it is perhaps impossible to obtain these in a pure 

 state, it is difficult to ascertain the exact connection between 

 the various unaltered and altered products. 



Having given a general account of the various colouring 

 matters met with in foliage, I will now proceed to show how 

 they serve to give rise to the almost endless variety of 

 autumnal tints. These are usually due to varying mixtures 

 of colours belonging to two or more groups. It is very 

 doubtful if any leaves are coloured by one single substance, 

 and generally they contain not only colours belonging 

 to several groups, but even more than one of the same 

 group. 



Unfaded green leaves are coloured mainly by chlorophyll, 

 but the tint is very much modified by xanthophyll, and by 

 colours of the chrysophyll group. The presence of these, 

 in varying relative and absolute amount, explains in a most 

 satisfactory manner all the various brighter and darker 

 greens met with in different leaves in different conditions. 

 It is doubtful if chlorophyll has ever been seen free from 

 xanthophyll. On heating green leaves with alcohol, a bright 

 green solution is obtained. On agitating with bisulphide of 



