Evolution of Plants 319 



culminated in the highest batrachospermoid, rhodomeloid, 

 and ceramioid divisions. 



If now we compare numerically the living species of Rhodo- 

 phyceae that show simplest cellular structure, simplest chro- 

 matophore conditions, and simplest asexual as well as sexual 

 reproduction Tsdth those that are decidedly complex in all 

 of these points, it is seen that the class naturally divides itself 

 into a smaller section mthin which fall the Bangiacese in mdest 

 sense, the Helminthocladieae, the Thoreacese, and related 

 smaller famihes. The larger section includes the ordinary 

 red marine algse. Now in the former section are 10 genera 

 and 69 species that are wholly or in great part fresh- water, 

 and 8 genera with 51 species that are marine. Such would 

 suggest that there is at least as much evidence for a fresh- 

 water origin of the whole group as for a marine. 



In the latter and much larger section 291 genera and 1975 

 species are wholly marine, for, while Bostrychia Moritziana 

 and a few Delesserias may at times occur in and show capacity 

 for fresh-water life, all indications are that they are temporary 

 or adaptive migrants from the seashore. 



Examining the two sections more in detail as to individual 

 structure, chromatophore formation, and methods of reproduc- 

 tion, added points of interest appear. Thus, from the short 

 or elongated cellular threads that make up the plant body 

 in some chamsesiphoneous algse, transition -is got to Aster o- 

 cijsiis and Goniotrichum in which more abundant branching 

 and expansion occur. From these the transition to Bangia 

 and Erythrotrichia in their young state is easy, while the later 

 subdivisioQ of their threads into multicellular cords, or flat 

 or branched expanses, leads up to Chantransia, Batrachosper- 

 miim and species of Lemanea. It seems also to be generally 

 true for the fresh-water species, as for the marine ones that 

 grow between or slightly below the zone of battering tidal 

 action, that the thallus remains filiform, slippery, and often 

 much branched. In deeper marine species, where the plants 

 grow amid less agitated surroundings, a more expanded and 

 usually flattened thallus is often formed. 



In chromatophore development the simplest and most primi- 

 tive evidently is seen in Goniotrichum, where instead of being 

 peripherally placed, as in Cyanophycese, the single chroma- 

 toi)hore has assumed a central position, but sends out radiating 

 arms toward the periphery. In Bangia and allies it is simi- 

 larly })laced, but the star-arms become more extended, and 

 at the periphery of the cell form longitudinal bands which 

 run in the peripheral protoplasm. In Chantransia, Nemalion, 



