THE RED GROUPS OF ALGJ2, 39 



agreeing with that occurring in Oscillatoria ; but in all these 

 cases the pink and red phycoerythrins are the chief coloured con- 

 stituents, whereas they are almost or quite absent from Oscil- 

 latoria. 



The Batrachospermae differ little, if at all, from such marine 

 Algae as I have just named. 



An Alga which grows abundantly in some of the small streams in 

 the neighbourhood of Sheffield, which Mr. Archer says is Lemanea 

 Jluviatilis, is a far better example of a connexion between the two 

 great divisions, but yet differs strikingly from both. It contains 

 a very considerable amount of a substance giving the same general 

 spectrum as the purple phycocyan of Oscillatoria, which, however, 

 is decomposed at a very considerably lower temperature. Lemanea 

 also differs in containing a relatively far less amount of red phy- 

 coerythrin than the more typical red marine Algae, and, in addition 

 to the pink phycoerythrin, appears to contain a considerable quan- 

 tity of the same pink phycocyan as that found in Oscillatoria. It 

 is thus, on the whole, an excellent case of a connecting-link ; and 

 probably further research will enable us to detect other species 

 more completely filling up the gaps. Palmella cruenta agrees with 

 the Florideae in containing much pink phycoerythrin. So much yet 

 remains to be learned, that it would be altogether premature to 

 speculate on the bearings of such facts. In former papers* I have 

 shown that many important changes in the colouring-matters are 

 brought about by a variation iu the amount of light in which the . 

 plant grows ; and such changes must be more fully studied before 

 we can form any very definite conclusions. There is also another 

 most important branch of inquiry which requires much further 

 study. In my paper published in the ' Monthly Microscopical 

 Journal ' 1 1 have shown that there is in some cases an intimate 



i 



connexion between the spectra of closely related substances, and 

 that, when spectra differ only in wave-length, there is probably 

 some relation between the two substances. The further examina- 

 tion of this question may throw much light on the mutual relations 

 between the various colouring-matters found in Algae. Thus, fo£ 

 example, it appears extremely probable that the pink phycocyan 

 of Oscillatoria may be chemically changed into the pink phyco- 



* Proc. Roy. Soc. vol. xxi. p. 442 ; Quart. Journ. of Science, vol. iii. (N. S.) 



p. 451. t Vol aii. p. 198. 



LINN. JOUltN. — BOTANY, VOL. XT. 



£ 



