Marine Algce of Berwick-on-Tweed. 371 



32. Fronds slimy, composed of an axial layer of elongated filaments and a 

 distinct cortical layer of short, horizontal filaments. ... 33 



Fronds composed of elongated internal cells, which become smaller at 

 the surface. ... ... ... ... ... ... 35 



Fronds, at least in the younger portions, formed of cells of nearly 



uniform length, arranged in transverse bands, without any proper 

 cortical layer. ... ... ... ... ... ... 38 



33. Fronds tough and dense. ... ... ... Chordaria. 



Fronds soft and flaccid. ... ... ... ... 34 



34. Outer cells of cortex producing plurilocular sporangia. Gastagnea. 



Outer cells of cortex not producing plurilocular sporangia. Mesoglosa. 



35. Fronds traversed by a central filament formed of large cylindrical 



cells placed end on end, sporangia inconspicuous, formed from the 

 cortical cells. ... ... ... ... ... Desmarestia. 



Fronds destitute of distinct axial filament. ... ... 36 



36. Fronds simple, more or less beset with pellucid hairs, spores formed 



from the cortical cells. ... ... ... Litoaiphon. 



Fronds branching. ... ... ... ... ... 37 



37. Unilocular sporangia covering the surface in dense patches, at maturity 

 projecting above the surface of the frond. ... Stictyosiphon. 

 Unilocular sporangia scattered, immersed. ... Dictyosiphon. 



38. Fronds minute, ending in a hyaline hair, monosiphonous below, densely 



beset above with very short branches, between which are the 

 sporangia. ... ... ... ... ... Myriotrichia. 



Fronds ending in a large, single cell, the cells of the lower part giving 

 off descending filaments, which become interwoven and form a false 

 cortex. ... .. ... ... ... ... 39 



39. Rhizoidal filaments few and limited to the base of the plant, branching 

 irregularly pinnate. ... ... . Sphacelaria (in part). 



Rhizoidal filaments numerous. ... ... ... 40 



40. Fronds distichously pinnate, sporangia on the secondary pinnate 



branches. ... ... ... ... Sphacelaria (in part). 



Fronds distichously pinnate, sporangia on short special branches 

 arising from the cortical layer of the main axis. Chcetopteris. 



branches whorled. ... ... ... .. Cladostephus . 



41. Fronds simple or occasionally proliferous. ... ... 42 



Fronds branching. ... ... ... ... ... 46 



42. Midrib present. .. ... .. .., Alaria. 



Midrib wanting. ... ... ... ... 43 



43. Fronds thin, subsessilu. ... .. ... ... ... 44 



Fronds thick and coriaceous, distinctly stipitate. ... ... 45 



44. Sporangia densely covering the surface of the frond. Phyllitis. 



Sporangia immersed or partly immersed in the frond, in scattered 

 spots. ... ... ... ... ... Punctaria. 



45. Cryptostomata present, stem flat, arising from a hollow warty 

 base. ... ... ... ... ... Saccorhiza. 



Cryptostomata wanting, stems cylindrical, attached by branching 

 rhizoids. ... ... ... ... ... Laminaria. 



