1871J Various Tints of Autumnal Foliage. 65 



In the first place, I must say that it appears very 

 desirable to divide the various colouring matters into 

 different groups or genera, each of which includes a number 

 of distinct substances or species, having some well-marked 

 peculiarity in common. I shall not attempt to give anything 

 like a complete account of the characteristic difference of the 

 various species, since that would involve a long and tedious 

 description of minute particulars, and shall confine my 

 remarks to such prominent facts as are of importance in the 

 subject more especially before us, and can be described 

 without illustrations or very technical notation. I scarcely 

 need say that such an inquiry could not possibly be carried 

 out by any other than the spectrum method. Chemical 

 analysis would be of very little use, and might easily lead us 

 to conclude that different substances were the same, and the 

 same different. It also is especially useful in studying the 

 complicated mixtures with which we have to deal, since 

 particular substances can be easily recognised when it would 

 be quite impossible to obtain them in a separate state. For 

 a more complete description of this method of research I 

 beg to refer to what I have already published on animal and 

 vegetable colouring matters,* and on some technical appli- 

 cations of the spectrum microscope. 4 - I may also say that, 

 spending, as I do, several hours nearly every day amongst 

 the woods, fields, and moors, I have had good opportunity 

 for studying the application of such inquiries to the subject, 

 before us. 



The group of colouring matters which first of all claims 

 our attention is that which may be distinguished by the 

 term chlorophyll. It has often been treated as if it were one 

 simple substance, but optical examination proves the 

 existence of a number of separate species. The leaves of 

 most plants are coloured green by a mixture of two or more 

 of these. One kind occurs in a state of comparative purity 

 in the small aquatic plants allied to Oscillaria, and the green 

 leaves of trees appear to contain this along with one which 

 gives special absorption-bands. Another is the product of 

 the action of acids on these, and occurs naturally in some 

 leaves, especially when turned brown in autumn, and this 

 gives rise to a very special spectrum with numerous bands. 

 A fourth, found in faded Conferva, is closely related to the 

 last, but differs in gradually turning to a deep blue colour, 

 when hydrochloric acid is added to the alcoholic solution. 

 All these have the following peculiarities in common — they 



* " Proceedings of Royal Society," vol. xv., p. 433. 



•f- "Quarterly Journal of Microscopical Science," New Series, vol. ix., p. 358. 

 VOL. VIII. (O.S.) — VOL. I. (N.S.) K 



