452 Comparative Vegetable Chromatology. [October, 



describe the different coloured substances formed by the 

 constructive energy of living plants, or changes that take 

 place in them whilst they are still portions of living 

 organisms, which changes can be imitated very imperfectly, 

 and I shall only incidentally notice alterations which occur 

 after the plants are dead. 



When first I commenced the study of the colouring 

 matters, I was very well contented to confine my attention 

 to those which occur in relatively large quantity in flowers 

 and green leaves, or give striking and well-marked spectra. 

 On extending my researches to fungi, lichens, and algae, I 

 soon found that the more abundant substances were very 

 different in different classes of plants ; and on making more 

 careful comparisons, I found that some of the colouring 

 matters which occur in a relatively large quantity in one 

 class are often not really absent from others, but occur in 

 relatively small amount. This led me to discover that the 

 coloured solutions obtained from green leaves are even more 

 complex than had been supposed, and that, independent of 

 those soluble in water, they contain normally no less than 

 six or seven coloured substances, perfectly well distinguished 

 by their optical and chemical characters. Having deter- 

 mined the chief coloured constituents of the leading classes 

 of plants, I drew up a rough table, showing their distribu- 

 tion through the great groups of the vegetable kingdom, and 

 saw at once that there was such a striking connexion 

 between the general organisation of plants and the character 

 of the colouring matters contained in them, that it was 

 desirable to explore the question as completely as possible. 

 This inquiry would have been very difficult, if not impos- 

 sible, if I had not been able to contrive fresh means for 

 separating or otherwise recognising the different constituents 

 of complex mixtures. 



Many of the most important coloured substances met 

 with in plants are insoluble in water, but soluble in 

 bisulphide of carbon and in alcohol, but the relative facility 

 with which they are dissolved by these two reagents differs 

 very much. When dissolved in spirits of wine of the usual 

 strength, and the solution agitated with excess of bisulphide 

 of carbon, the whole of some of them is carried down in 

 the bisulphide, whereas the whole of some other substances 

 is left in the alcohol if it be strong, but more and more is 

 carried down in the bisulphide when the alcohol is more and 

 more diluted with water. The result is that some substances 

 can be separated perfectly, and others only partially ; but by 

 agitating the solution in spirit with excess of bisulphide, 



