COLOURS OF FADED LEAVES. 33 



normal eyes to conceive the possibility of so great a 

 defect. 



The brilliant tints exhibited by the decaying foliage of 

 the trees in this neighbourhood in the course of the 

 autumn, forming a chromatic display such as those living 

 near manufacturing towns have few opportunities of wit- 

 nessing, have led me to think a little on the cause of the 

 formation of these colours and its possible connexion with 

 chlorophyll, on the chemistry of which I have lately been 

 making some experiments. 



The colour of the leaves of plants is a phenomenon which 

 is probably never quite stationary at any period of their 

 development. When lying rolled up in the leaf-bud they 

 are, like underground shoots and other parts of plants 

 that have not been exposed to light, almost white ; never- 

 theless they already contain a colouring-matter called 

 etiolin, the alcoholic solution of which is yellow and shows 

 absorption-bands similar to those of chlorophyll. Whether 

 this etiolin on the leaf unfolding passes over into chloro- 

 phyll and whether it continues to be formed during the 

 further stage of development is not known. All we know 

 is that when the leaf expands it immediately becomes 

 green from the formation of chlorophyll. It is, however, 

 evident that more than one colouring-matter is formed 

 after exposure of the leaves of plants to light. The colour 

 due to chlorophyll alone is probably seen in its purest state 

 in the tender exquisite green of the young beech leaf or 

 blade of corn. Other leaves, such as those of the oak, 

 before attaining maturity have a decidedly yellow tinge, 

 due, it is supposed, to the presence of an unusual propor- 

 tion of phylloxanthin, the yellow colouring-matter always 

 accompanying chlorophyll. Indeed the lively contrast of 

 tints seen in the foliage of the woods in early spring, the 



SER. III. VOL. VIII. D 



