38 



MR. H. C. SOKBY ON THE COLOUHING-MATTKKS Of 



is shown by the wave-length of the light at that part of the 

 spectrum in millionths of a millimetre, and their width by the dif- 

 ference between the wave-lengths of the opposite sides when the 

 the bands are well defined. The lowest temperature at which 

 each of the substances is slowly decomposed when dissolved in 

 syrup is given in degrees Centigrade. 









Name of substance. 



Centre. [Width J Fluorescence. 



Decomposed 

 at 



Blue phycocyan, Oscill. 

 Purple phycocyan, Os. 



> 



'» 



ii 



Porph 



Pink phycocyan, Os 



Pink pliycoerythrin, Par. 

 Red pliycoerythrin, Por. . 



621 

 021 

 567 



569 



497 



18 



32 



32 

 29 

 18 

 27 



Strong red. 

 Strong rose. 



II 



Doubtful. 

 Strong orange 

 . None. 



7.~>° C. 

 SO 



G8 



65 



80 

 80 



These different substances are also decomposed in a varying 

 manner by alcohol of various strength ; and the results of the 

 study by that means agree with those arrived at by heating 

 the solutions as described. 



The chemical and physical relations of these colouring-matters 

 of Algse are so remarkable that I feel much tempted to enter 

 into them more fully, but forbear, since I am more particu- 

 larly anxious to consider their distribution in the different groups 

 of the plants. The two principal colouring-matters of Oscillatoria 

 soluble in water are entirely different from the two most character- 

 istic of the Floridere a3 found in such examples as Schizymenia 

 edulis. With the exception of the blue chlorophyl common to 

 all, the other colouring-matters belonging to the xanthophyi 

 group are equally distinct ; so that the OscillatoruB and the Flo- 

 ridese are as well distinguished by their chromatological charac- 

 ters as by their general structure. Perhaps in some cases they 

 have traces of some substances in common ; and there are well- 

 marked connecting-links. For instance, Cystoclonium purpuras- 

 cens and Polysiphonia elongata contain a small quantity of either 

 purple phycocyan or some substance closely allied to it, which is 

 the cause of their more purple tint ; and Porphyra vulgaris, be- 

 sides this, contains some blue phycocyan closely, if not absolutely $ 



