458 Comparative Vegetable Chromatology. [October, 



of the chlorophyll being almost equal. This red colouring 

 matter is probably a product of the decomposition of 

 chlorophyll, due to the action of light, when the leaves are 

 in a peculiar low state of vitality. The result of such a 

 predominating influence of what may be called accidental 

 substances is that mere colouring is often of very little 

 general significance, even in distinguishing closely allied 

 species. This is, however, quite intelligible, since com- 

 paratively small special differences in the constitution of the 

 individual plants may suffice to alter the character of the 

 accidental colouring matters, especially in organs like the 

 petals, which are not essential for the life of the individual 

 plant. In fact, by artificially lowering the constructive 

 energy, by screening flowers from the light, I have succeeded 

 in producing as much change as would have corresponded 

 to well-marked varieties, if both had been exposed to the 

 light. When, however, careful qualitative and comparative 

 quantitative analysis are compared, which appears to me to 

 be the only correct way of studying the subject, it becomes 

 quite apparent that there is a very interesting connection 

 between the distribution of the fundamental colouring 

 matters and the general organisation of plants. In pro- 

 ceeding from the lowest to the highest classes there is an 

 unmistakable advancement from a type corresponding in 

 certain particulars with that of some of the lowest animals 

 to that of the highest classes of plants, as though certain 

 colouring matters were more characteristic of, and perhaps 

 indeed essential for, the healthy growth of the most perfect 

 and specialised types of vegetable life. There are also re- 

 markable examples of the changes in the colouring of par- 

 ticular plants, according as they grow in strong light or in 

 such very shady situations that the vitality is very low, and 

 on comparing the qualitative and quantitative differences it 

 may be seen that in several important particulars they 

 correspond with the differences met with in higher or 

 lower classes, the effect of the comparative absence of light 

 being to lower, and the effect of the presence of extra light 

 being to raise the type. The most striking instance of this 

 so far met with is in the case of Oscillatorice ; for when they 

 grow where the light is so feeble that they can only just keep 

 alive, the type of their colouring approximates to that of 

 olive Alga, whereas, when they grow exposed to much air 

 and light, the type approximates very closely to that of such 

 lichens as Peltigera canina. 



In order to show the kind of evidence on which such 

 conclusions are based, and also to illustrate what I mean by 



