1873.] 



Comparative Vegetable Chromatology . 



46] 



almost free from the other. On the contrary, when we have a mixture 

 of two more extreme, a very considerable quantity of one is left when 

 the other has disappeared. 



I fear it will be difficult to find any other snch series of very similar 

 colouring-matters ; but if, on further investigation, such a connexion 

 between the rate of decomposition and the absorption of light turn out to 

 be a general law, it will be an additional proof of some kind of connexion 

 between chemical and optical characters. The most striking modifi- 

 cation of this rule that I have so far met with, is in the case of phyco- 

 xanthine and orange xanthophyll when mixed with chlorophyll in solution. 

 When alone, dissolved in a mixture of alcohol and bisulphide of carbon, the 

 phycoxanthine is so much more rapidly decomposed by bright sunlight than 

 the orange xanthophyll that the relative amount of the latter is soon 

 increased to double the original, as determined by separating them from 

 one another ; whereas if a considerable quantity of blue chlorophyll be 

 present, the very opposite result occurs, as proved by comparative ana- 

 lysis. Here, then, we have a most striking effect of the presence of the 

 chlorophyll, which itself was more rapidly decomposed than either of 

 the other substances mixed with it. Having only very recentlv esta- 

 blished this fact, I have not yet been able to decide whether it is due to 

 the loss of the energy in decomposing the chlorophyll of those rays of 

 light which, in its absence, would have been instrumental in decom- 

 posing the phycoxanthine, or whether it depends upon some chemical 

 action connected with the presence of the changing chlorophyll ; but it 

 seems to me that we have in such a case the first example of a new 

 branch of inquiry, which can hardly fail to be of value in explaining the 

 influence of chlorophyll in the growth of plants. Many facts seem to 

 prove that one substance may protect another by absorbing the active 

 rays or by consuming the oxygen, which, in its absence, would decom- 

 pose the other. 



Fucoxanthine. 



This is the name I propose for the principal colouring-matter of Fuel 

 and other olive Algce. It may be obtained in the manner already de- 

 scribed, only that in order to separate it from the chlorofucine, after 

 separation of all the chlorophyll, a few drops of ammonia should be 

 added to the alcoholic solution, and the whole diluted with an equal bulk 

 of water. The bisulphide of carbon is then precipitated with almost all 

 the fucoxanthine, whilst nearly the whole of the chlorofucine remains in 

 the dilute alcohol. As thus purified, fucoxanthine dissolved in bisulphide 

 of carbon is of a beautiful amber colour, and its spectrum shows two 

 obscure absorption-bands, the position being intermediate between those 

 of orange xanthophyll and xanthophyll, so that a mixture of these gives 

 nearly the same spectrum. The difference, however, is completely proved 

 by other facts. The bands of fucoxanthine are much less raised bv 

 alcohol and other liquids of high band-raising power than the bands of 



