80RBY S RESEARCHES ON CHROMATOLOGY. 105 



tical with those in Fucus and other olive Algce, whereas when 

 grown exposed to much sun there is a great reduction in the 

 amount of those substances which are so characteristic of that 

 group, and at the same time a great developement of others which 

 are almost or altogether absent from it, but occur in large quantity 

 in, and are very characteristic of, such lichens as Peltigera canina. 

 The olive Algce are, however, distinguished from those Oscillatorice 

 which approach them most closely by the absence of the phyco- 

 cyans ; and though these occur in Peltigera, it is distinguished by 

 the absence of fucoxanthine from those Oscillatorice which in other 

 respects agree with it. We may also draw another important con- 

 clusion from the above facts. Oscillatorice approach most closely 

 to the olive Algai 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 Algw, one leading 

 gradually to the green Algce through Porpliyra, 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 xanthophyll make their appearance 

 — at least I have hitherto met with no good connecting links con- 

 taining 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 phy- 

 cocyans excludes yellow chlorophyll and yellow xanthophyll. Curi- 

 ously enough this break does not occur between one great natural 

 class and another, but in passing from those red Alga? 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 dis- 

 tribution of the colouring-matters ; and this could hardly be ex- 

 pected 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 

 arrangement 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 



