108 SEAWEEDS 



form and division of one initial cell (or at most a 

 small group) derived from the epidermal layer. 



The Reproductive Organs, both unilocular and pluri- 

 locular, are either differentiated superficial or epi- 

 dermal cells or outgrowths of these. They are 

 accompanied or succeeded, as has been noted above, 

 by the formation of paraphyses. While in such 

 genera as Desmotrichum, Punctaria, &c., the epi- 

 dermal cells in question undergo but little differ- 

 entiation, in Scytosiphon, Hydrodathrus, and other 

 genera, the cells giving rise to plurilocular sporangia 

 undergo considerable elongation and division in the 

 process. The globular unilocular sporangia of Asper- 

 ococcus, standing free from the surface of the plant 

 among paraphyses, originate in outgrowths from the 

 epidermal layer as the paraphyses do. 



The order is formed of three others recognised 

 formerly as Punctariaccm, Scytosiphonacew, and Asper- 

 ococcaccce, together with the genera Ooilodesme and 

 Myd&phycus a grouping of them justified by Kjell- 

 man (Engler and Prantl's Nat. Pflanzcnfamilicn, 

 part i., p. 197). 



The Geographical Distribution is fairly even through- 

 out all seas, but more abundant in temperate waters. 

 Desmotrichum, Punctaria, Litosiphon, Scytosiphon, 

 Phyllitis, and Asperococcus occur in British seas. 



RALFSIACE^:. 



General Characters. This small order embraces 

 plants of a very undifferentiated vegetative structure 

 and of a crust-like habit. The reproductive organs 



