1873.] 



Comparative Vegetable Chromatology. 



443 



scopic instruments designee! for the purpose, but yet it cannot be looked 

 upon as being either chemistry or spectrum-analysis. It is also requisite 

 to make use of light as a reagent, and yet the subject could not be called 

 photography or even photo-chemistry ; and though most intimately con- 

 nected with biology, it could scarcely be regarded as a branch of that 

 science. It appears to me most desirable to adopt some name for the 

 whole subject, including whatever modifications of other branches of 

 science are requisite for its efficient study, and none would meet the 

 requirements of the case better than Chromatology. I trust that the facts 

 I am about to describe will be sufficient to show that we have such a 

 wide branch of science before us that it deserves some special name. 

 Then, again, since I now purpose to describe the points of agreement 

 and difference in the colouring-matters of various classes of plants, it 

 appears to me that no better title could be adopted than the one I have 

 chosen, viz. Comparative Vegetable Chromatology. 



My attention has been for a long time directed to the colouring- 

 matters of plants, but it is only within the last year that I have dis-. 

 covered the means of carrying out the inquiry in a satisfactory manner, 

 and convinced myself that the most valuable conclusions are to be learned, 

 not by looking for the rarer or more attractive substances which give 

 remarkable spectra, but from the qualitative and quantitative determina- 

 tion of the different coloured constituents of complicated mixtures, some 

 of which substances have no striking properties, and might easily be 

 overlooked, though perhaps of great importance in connexion with the 

 life of particular plants. The successful carrying out of this inquiry 

 will necessarily be the work of years ; for not only is the whole field 

 comparatively unexplored, but it will be requisite to examine ail 

 classes of plants and many of animals, at various seasons of the year 

 and when growing in different natural and artificial circumstances, and 

 also to study the relation of the different colouring-matters to one 

 another, and the action on them of light and chemical reagents. In 

 every department of the subject very interesting questions remain to be 

 answered ; and the following paper must be looked upon merely as a 

 general outline of what I have hitherto been able to learn, and as an 

 indication of what may be expected to result from further research. 



The Absorption-band-raising Power of Solvents. 



The identification of the individual colouring-matters has been effected 

 by means of their spectra, sometimes as seen by examining the plants 

 themselves, but generally when dissolved in various liquids, with or with- 

 out the addition of appropriate reagents ; but any other peculiarities were, 

 taken advantage of, according to the circumstances of the case. For 

 further particulars connected with the general method I refer to my 

 former papers*. 



* Proc. Eoy. Soc. 1867, vol. xy. p. 433. Quart. Journ." of Microscopical Science, 



