175 
The margin is somewhat lobed, and the filaments of the 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 off 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. 
Petrocelis Hennedyi. A, basal layer seen from the under face (230:1). B, vertical section of border of frond. 
C, vertical section of older part of frond. B and C 390: 1. 
of the crust; in the upper part they are 4—6 y 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 are 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, subdichotomous or sometimes sympodial; the latter reminds 
one of the false ramification of the Cyanophyceæ, 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 
