370 Marine Algce of Berwick- on-Ttueed. 



25. Fronds irregularly globose, hollow, gelatinous, sporangia at the base 



of the coloured cortical filaments. ... ... Leathesia. 



Fronds cap-shaped, fruit in very long strap-shaped receptacles. 



Himanthalia. 

 Fronds forming crusts or expanded pellicles. ... ... 26 



Fronds small, tufted, composed of a dense basal portion and an outer 

 portion composed of free filaments. ... ... Elachista. 



Fronds tubular, unbranched. ... ... ... ... 27 



Fronds filamentous. ... ... ... ... ... 29 



Fronds membranaceous, expanded. ... ... ... 41 



26. Fronds membranaceous, lobed, attached by fibres issuing from its 

 lower surface, lobes free, fruit in external patches, unilocular sporangia 

 unaccompanied by paraphyses. ... ... ... Aglaozonia. 



Fronds coriaceous, not attached by fibres, adherent throughout, fruit 

 in external spots, unilocular sporangia accompanied by paraphyses. 



Pvalfsia. 

 Fronds minute, thin, formed of a basal horizontal layer of cells and 

 short vertical filaments, between which the sporangia are borne. 



Myrionema. 



27. Fronds simple, hollow throughout, substance thin. ... ... 28 



Fronds simple, cylindrical, somewhat cartilaginous, with numerous 

 diaphragms. ... ... ... ... ... Chorda. 



28. Sporangia densely covering the surface. ... ... Scytosiphon. 



Sporangia external in scattered spots. ... ... Asperococcus. 



29. Fronds capillary, branching, formed of a single row of cells. 

 (Monosiphonons.) ... ... ... ... ... 30 



Fronds cylindrical, solid or occasionally becoming partially hollow 

 with age. ... ... ... ... ... . . 32 



30. Primary branches creeping in the substance of other algae, secondary 



and fructifying ramuli erect. ... ... ... Streblonema. 



Primary and secondary branches erect. ... ... ... 31 



31. Both unilocular and plurilocular sporangia formed by transformation 

 of special branches, plurilocular sporangia in the form of pod-like 

 branches, unilocular globose, sessile or shortly stalked. Ectocarpus. 

 Both forms of sporangia formed from the cells in the continuity of 

 the branches and not by a transformation of special branches. 



Pylaiella. 

 Filaments partly polysiphonous, unilocular sporangia partly immersed 

 in the frond, plurilocular sporangia formed by direct transformation 

 of the cells of the branches. ... ... ... Isthmoplea. 



branched and radiate from a central point, the spores are borne in large 

 sporangia, formed by the transformation of the joints. The sporangia at 

 length become free and are capable of growing by themselves and forming 

 new plants. The latter genus forms green patches on Flustrae, the 

 filaments being placed so close together that the plants appear to be almost 

 membranous, in this respect resembling Rhodochorton membrane ce.um. 

 The reproduction is by means of zoospores formed in the filaments. 



