40 ON THE COLOURS OF FADED LEAVES. 



similar to those of the substance from elm leaves. No tannin, 

 however, could be detected in the solution ; and this may 

 serve to explain the fact that blades of grass, corn, &c. do 

 not ultimately become brown in fading, but remain yellow. 

 The portion of the residue after evaporation left undissolved 

 by water, was green and fatty ; and its solution in alcohol 

 showed the absorption-bands due to modified chlorophyll. 



These experiments leave the question of the nature and 

 mode of formation of xanthophyll undecided. It may be 

 one and the same substance in all leaves, or it may differ 

 according to the source whence it is derived ; it may be 

 formed by the oxidation of chlorophyll, or it may preexist 

 in the green leaf. I am inclined to think that it exists ready 

 formed in the green leaf, but is not then seen on account 

 of the far greater tinctorial powers of the chlorophyll 

 present at the same time, and that it makes its appearance 

 only when the chlorophyll has been decomposed, the sole 

 trace left by the latter being the slight greenish tinge which 

 all faded yellow leaves show more or less. The varying 

 proportion of xanthophyll contained in green leaves would 

 explain the fact, difficult to understand if we suppose it to 

 be derived from chlorophyll, that some leaves assume a deep 

 yellow colour in fading, while others remain of a pale yellow, 

 and others again are almost colourless when they fall. 



I will now conclude, hoping that, if I have not commu- 

 nicated any thing strikingly new, I have at least succeeded 

 in affording the Meeting a few moments' amusement. 



Broinley, Kent, 



i oth December, r88i. 



