206 Dr. F. E. Fritsch. On the Subaerial and [Jan. 2, 



mucilage are far commoner in the uplands than in the lowlands, where the 

 risks of desiccation are much greater (see also below).* Secondly, we find 

 the subaerial growth of Cyanophyceee developed in situations which are often 

 exposed to a strong light and the presence of a second colouring matter 

 (phycocyanin) side by side with the chlorophyll, undoubtedly suits them to 

 an existence under such conditions. The presence of this additional pigment 

 shifts the assimilation-maximum,f but the phycocyanin, no doubt, also acts as 

 a kind of screen to the chlorophyll, although the exact modus operandi remains 

 an open question. The great variety presented by the colour of the cell- 

 contents in the Cyanophycese is familiar to all, yet we know practically 

 nothing about the meaning of these diverse shades of pigmentation. 

 GaidukovJ has experimented with Oscillaria from this point of view, and has 

 shown that the colour assumed by the cell-contents is complementary to that 

 of the supplied light, and that variation of the colour of the latter induces 

 corresponding changes in the colour of the Osc^arm-filaments. So that in 

 addition to the screening action§ of the phycocyanin it probably plays some 

 other important part in adapting the blue-green group to varying types of 

 illumination. The absence of any protective pigment is, no doubt, one of the 

 main causes of the lack of green algal forms in the subaerial vegetation, 

 although the rapid growth of the hardy blue-green element certainly 

 contributes very considerably to crowd them out. Mosses and Liverworts 

 are also mostly wanting in localities exposed to the strong light, although 

 they get on well enough as epiphytes on the tree-trunks in the moist shady 

 jungles and forests. It is interesting to notice in this connection that the 

 only member of the green Algse, which really competes successfully with the 



* Cf. also Gomont, " Myxophycece hormogonece " (in J. Schmidt., " Flora of Koh Chang "), 

 * Bot. Tidsskrift., 5 vol. 24, 1901-2, p. 203. He remarks : " Si l'on examine le catalogue que 

 nous en donnons, on s'apergoit immediatement que les Algues a gaines epaisses et colorees 

 l'emportent de beaucoup par le nombre des especes et par leur frequence. Ainsi, tandis que 

 les genera Oscillatoria, Lyngbya, Phormidium, Jlydrocoleum, ne sont represented chacun 

 que par une espece, les Scytonema et Stigonema en renf erment treize a eux seuls . . . 

 cette absence n'est pas purement accidentelle, mais, ainsi qu'on l'a maintesfois observe^ 

 les plantes les mieux adaptees aux regions tropicales sont celles qui trouvent dans 

 l'epaisseur, la consistance ou la coloration de leur gaine une protection contre les 

 s6cheresses frequentes et l'intensite de la lumiere." 



t See Pfeffer and Ewart, 'The Physiology of Plants/ vol. 1, Oxford, 1900, pp. 343—344. 



% " tlber den Einfluss farbigen Liclits auf die Farbung lebender Oscillarien," ' Anhg. z. 

 Abh. Kgl. Preuss. Ak. d. Wissensch.,' 1902 ; " Weitere Untersuchungen iiber den Einfluss 

 farbigen Liclits auf die Farbung der Oscillarien," ' Ber. Deutsch. Bot. Ges./ vol.21, 1903, 

 p. 484 et seq. 



§ In many cases the cell-contents no doubt obtain additional protection from the 

 intense light in the sheaths of the filaments, which are very frequently brown, yellow, or 

 red in colour. The colour of the sheath is also subject to much variation (cf. the first 

 footnote on this page). 



