COLOURS OF FADED LEAVES. 39 



a thick curdy precipitate with gelatine and an abundant 

 deposit on the addition of a mineral acid. On again eva- 

 porating the solution in the water-bath some decomposition 

 evidently took place ; for on adding water to the residue a 

 quantity of matter in the form of brown powder remained 

 undissolved. It is almost certain that it is the same process 

 of decomposition going on in the yellow leaf on exposure to 

 air and moisture that causes the colour to change to brown. 

 I think it probable that the process is one of oxidation, 

 and that it affects the tannin of the leaf or the solution 

 rather than the yellow colouring-matter ; for it is well 

 known that watery solutions of tannin undergo decompo- 

 sition, accompanied by change of colour from light to dark, 

 on exposure to air, especially when the solutions are hot. 

 This simple experiment shows that the yellow colour of 

 faded elm leaves is due partly, perhaps chiefly, to a yellow 

 colouring-matter soluble in water, partly to a yellowish 

 green substance consisting essentially of chlorophyll. The 

 former is, in my opinion, the true xanthophyll. 



In order to gain, if possible, a little more insight into 

 the process whereby the colour of green leaves changes to 

 yellow, I took an alcoholic extract of fresh grass, which 

 was of the usual bright green colour, and exposed it in a 

 window to the action of the sun and air. After some days 5 

 exposure it had undergone the well known and frequently 

 described transformation ; i. e. the bright green colour had 

 changed to a greenish yellow, and the solution, from being 

 opaque even in thin layers, had become transparent in con- 

 sequence of the oxidation of the chlorophyll contained in it. 

 Now this liquid, though not quite so yellow as the alcoholic 

 extract of faded elm leaves, was found closely to resemble 

 the latter. On evaporating over the water-bath and adding 

 water to the residue a yellow liquid was obtained, con- 

 taining a colouring -matter the reactions of which were 



