464 Comparative Vegetable Chromatology. [October, 



correspond to others in a more rudimentary state ; and if 

 the development be arrested by unfavourable conditions, 

 artificially produced, this rudimentary character of colouring 

 is retained when the petals are fully grown. One of the 

 most remarkable facts is, that in some cases, if w r e slowly 

 oxidise the mixed colouring matters dissolved out from a 

 flower grown in the light, by adding a little turpentine, or 

 by exposing the solution to the sun, the relative proportion 

 of the different substances is changed, so as to closely cor- 

 respond to that met with in the same kind of flower grown 

 nearly in the dark. Exposure to light thus produces the 

 same effect on the dead colouring matters that absence of 

 light produces in the living plant, which seems to show, 

 that, when the constructive energy is weak, those substances 

 which are most easily decomposed are not sufficiently pro- 

 tected from decomposition. The study of such changes 

 during the growth of other parts of plants cannot, I think, 

 fail to throw much light on several interesting questions. 



Such, then, is a brief account of some of the leading 

 features of what appears to me to be a very promising 

 branch of research. There are many questions connected 

 with it that I have alluded to in the most incidental manner 

 or not mentioned at all. The study of the action of light 

 on the various coloured substances when in different condi- 

 tions, and dissolved in different liquids, either when alone or 

 mixed with others, is of itself a wide field for inquiry, well 

 worthy of attention, since it may serve to explain the 

 manner in which the energy of the sun's rays becomes 

 stored up in the various compounds formed by plants. I 

 have studied this action very carefully, and though I have 

 been able to detect what appear to be general laws of much 

 interest in connection with optics and chemistry, very much 

 still remains to be learned. The chemical relations of the 

 various colouring matters require much further investiga- 

 tion, in order to ascertain whether and in what circum- 

 stances one may be artificially or naturally changed into 

 another, which is especially interesting in connexion with 

 the colour of the petals of flowers. It is also very desirable 

 that the connexion between the decomposition of carbonic 

 acid and the changes that take place in the colouring 

 matters when exposed to the sun, should be more fully 

 examined, since, when separated from the plants, their 

 decomposition by light seems to be a process of oxidisation, 

 which, of course, is the reverse of what occurs when living 

 plants absorb carbonic acid and give off oxygen. Perhaps 

 it is only those portions of the endochrome which in some 

 way or other have lost their normal power that are thus 



