1873.] 



Comparative Vegetable Chrom otology. 



477 



is distinguished by the absence of fucoxanthine from those Oscillatorice 

 which' in other respects agree with it. "We may also draw another 

 important conclusion from the above facts. Oscillatorice approach most 

 closely to the olive Algce when their vegetative energy is the weakest, 

 when so little light is present that they can only just keep alive. This 

 seems to show that the colouring of olive Algce, in some way or other, 

 belongs to a lower type than that of the green Algce, as indicated by other 

 facts previously described. 



General connexion of different classes of Plants. 



The olive Algce are thus connected with the lowest green plants by 

 means of two different groups of the red Algce, one leading gradually to the 

 green Algce through Porphyra, and the other to lichens through Peltigera. 

 There is the same sudden break in both, where the phycocyan and 

 phycoerythrine colours cease and yellow chlorophyll and yellow xantho- 

 phyll make their appearance — at least I have hitherto met with no 

 good connecting links containing a small quantity of both instead of a 

 normal amount of one or of the other ; and if this be really a universal 

 fact, it would seem to show that, in some way or other, the presence of 

 the phycocyans excludes yellow chlorophyll and yellow xanthophyll. 

 Curiously enough this break does not occur between one great natural 

 class and another, but in passing from those red Algce which are so 

 closely related to the green series as Porphyra, and from Peltigera to other 

 lichens. So much remains to be learned of the details that it would be 

 premature to put forward any general scheme with the expectation of its 

 being finally adopted ; but at the same time it may perhaps be well to 

 express what is already known, if only as a guide for further research. 

 Of course I refer simply to the distribution of the colouring-matters ; 

 and this could hardly be expected to depend upon, or accurately follow, 

 the difference in the development of the reproductive organs ; but, on the 

 contrary, it seems to represent something special in the constitution of 

 the plants, for which no name has hitherto been adopted, but which I 

 have called constructive energy. If such be really the case, an arrange- 

 ment founded on chromatological characters alone would by no means 

 necessarily agree in every particular with a natural system founded on 

 structural peculiarities. Taking into consideration the various facts 

 described above, the following arrangement expresses every thing so far 

 known respecting the distribution of the different colouring-matters : — 



Actiniae. 

 Anihea cereus, var. smaragdina. 

 Olive group of Algce. 



Red Algce. Oscillatorice. 



Porphyra. Peltigera. 



Green Algce. Lichens. 

 Higher Cryptogamia. 

 Highest classes of plants. 



