1873.] 



Comparative Vegetable Chromatology . 



451 



end of the spectrum, and following the order in which it retreats towards 

 the blue. This is, moreover, the order in which they are decomposed by 

 light, and also often that in which they vary in other important pecu- 

 liarities. I have chosen specific names which indicate the generic rela- 

 tions of the separate substances. 



Stokes's Researches. 



In the Proceedings of the Royal Society for 1864* there is a paper by 

 Professor Stokes, rather more than a page long, on the supposed identity 

 of biliverdin with chlorophyll, with remarks on the constitution of chlo- 

 rophyll, which, in my opinion, in the space of a few sentences contains 

 more valuable information on that subject than all other subsequent 

 papers put together. In this he says, " I find the chlorophyll of land- 

 plants to be a mixture of four substances, two green and two yellow, all 

 possessing highly distinctive optical properties. The green substances 

 yield solutions exhibiting a strong red fluorescence ; the yellow substances 



do not Green sea-weeds agree with land-plants, except as to the 



relative proportions of the substances present ; but in olive-coloured sea- 

 weeds the second green substance is replaced by a third green substance, 

 and the first yellow substance by a third yellow substance, to the pre- 

 sence of which the dull colour of those plants is due." No particulars 

 were given respecting the manner in which these different colouring- 

 matters had been separated, nor any description of their individual cha- 

 racteristics, and this is probably the reason why these statements have 

 had so little influence on subsequent researches. If I may judge from 

 my own experience, an experimenter might well have paid a great 

 amount of attention to the subject without being able to discover the 

 nature of the evidence which had led the author to adopt such conclu- 

 sions ; and it would require a very considerable amount of independent 

 discovery to enable any one to appreciate their real merit. As for myself, 

 I investigated the subject quite independently, and it was not until after 

 I had satisfied myself as to the real facts of the case that I compared my 

 results with those described by Stokes in the above-named paper, and 

 then saw that they corresponded in many of the most important par- 

 ticulars, though I have no doubt that I was led to them by studying a 

 very different class of facts. The principal green substance of the 

 author is manifestly my blue chlorophyll ; his second green substance 

 my yellow chlorophyll, and his third green substance my chlorofucine, 

 whilst his third yellow substance, found in olive sea-weeds, must be my 

 fucoxanthine. His other two yellow substances must, in some way or 

 other, represent the four yellow substances described by me as orange 

 xanthophyll, xanthophyll, yellow xanthophyll, and lichnoxanthine, with 

 perhaps a little of my orange lichnoxanthine. It will thus be seen that 

 my conclusions fully confirm what he has said respecting the compound 



* Yol. siii. p. 144. 



