175 



The margin is somewhat lobed, and the filaments of tlie basal layer radiate towards 

 the border of the lobes (fig. 92 A). When the surface of the substratum is uneven, 

 small rudimentary rhizoid cells may be given ofT from the basal layer (fig. 92 C). 

 Fusions between the cells of this layer have not been met with. The upright fila- 

 ments which are given off from the acroscopic end of the cells in the basal layer 

 are decumbent at the base, so that there often seem to be more than one layer 

 of basal cells. At the border the filaments are directed obliquely forwards. The 

 upright filaments have almost the same thickness in the upper and the lower part 



Fig. 92. 



Peti-ocelis Ilcnneilfii. A, l)asiil layer seen from tlie under lace (230:1). B, vertical section of border of frontl. 

 C, vertical section of older part of frond. B and C 390 : 1. 



of the crust; in the upper part they are 4 — 6 m thick. They are imbedded in a 

 glutinous intercellular substance which swells greatly in fresh water, whereby the 

 filaments are separated. The upper end of the filaments is nearly always a little 

 attenuated, the uppermost cell usually being narrower than the other, and more or 

 less conical, or the upper part of the filament is gradually tapering (fig. 95). In 

 some cases, however, particularly in thin crusts, I found the filaments of the same 

 thickness to the very end (fig. 96). The cells ar& usually twice or thrice as long 

 as broad, they contain a nucleus and a cap-shaped chromatophore with more or 

 less lobed border; in a specimen examined in July the cells contained numerous 

 small starch grains. The upright filaments are simple or little branched. The ra- 

 mification is lateral, subdicholomous or sometimes sympodial; the latter reminds 

 one of the false ramilication of the Cyanophycese, the penultimate cell growing out 

 and throwing aside the apical cell, which does not usually develop further. In 

 fig. 93 B the wall of the outgrowing cell is seen to have been burst. Hyaline 



