70 Various Tints of Autumnal Foliage. [January, 



carbon, this sinks to the bottom with the greater part of the 

 chlorophyll and some xanthophyll in solution, whilst the 

 alcohol retains most of the xanthophyll and some chloro- 

 phyll. After agitating this with a little fresh bisulphide, 

 evaporating to dryness, and dissolving out the chrysophyll 

 by water, when dry, the impure xanthophyll may be dissolved 

 in bisulphide of carbon. The solution of chlorophyll in the 

 bisulphide first obtained may be somewhat purified by 

 agitating with fresh alcohol, but even then the spectrum 

 clearly shows the absorption-bands due to xanthophyll. 

 Still, on comparing the two different products, we can see at 

 once that an approximate separation has been effected, and 

 that for an equal amount of chlorophyll one contains six or 

 eight times as much xanthophyll. This is a mere green- 

 yellow, and the other a bright green ; but, since it must be 

 made considerably brighter by the xanthophyll, pure chloro- 

 phyll is no doubt of a darker and bluer green colour. The 

 tint of many green leaves is also much modified by various 

 colours of the erythrophyll group, which give rise to more 

 or less green browns, and in some cases almost to black; for 

 the green chlorophyll absorbs the blue and red rays, and the 

 erythrophyil the green, so that all light is extinguished. If 

 the erythrophyll preponderates over the chlorophyll, we have 

 a red or even purple green, as in the case of the copper and 

 purple beech ; and thus, independent of any change, there 

 is a considerable variation in the tints of normal growing 

 leaves. It is, however, in autumn, when the chlorophyll 

 has disappeared, that the brighter and more definite colours 

 are produced. The amount of xanthophyll which is found 

 in green leaves is so considerable, that probably the yellow 

 colour of faded leaves is quite as much, or even more, due 

 to that which previously existed than to any specially 

 developed in the change, and the alteration may be said to 

 consist chiefly in the disappearance of the chlorophyll. The 

 result of this is that a deep green is changed into a bright 

 yellow, and the general change in the spectrum is that there 

 is no longer any absorption at the red end. Probably, how- 

 ever, few yellow leaves are coloured merely by xanthophyll, 

 and the tint of many depends quite as much on the chryso- 

 phyll, and is also very much modified by colours of the 

 erythrophyll and phaiophyll groups. 



As I have already named, many leaves contain colour of 

 the erythrophyll group, even when young and healthy, but 

 the production of a red colour is more common in autumn, 

 when their vitality is diminished. In some cases it takes 

 place whilst the chlorophyll is unchanged, or only partially 



