PH AOPHYCEZ 111 
SPHACELARIACEE. 
General Characters—The thallus consists of erect 
shoots springing from a more or less extensive basal 
creeping cushion fixed to the substratum. The erect 
shoots are more or less branched and may be as in 
the most reduced case a simple cell-row, or an articu- 
lated filament consisting below of tiers of cells of 
equal height, or the latter case may be further 
developed by the addition of a cortical tissue. 
Growth in length is effected by an apical cell. The 
reproductive organs are both unilocular and _pluri- 
locular and are borne on short branches. Vegetative 
propagation hy gemmee occurs. 
The Thallus—The most simple form is to be 
found in the exceptional case of Battersia mirabilis, 
for the inclusion of which the definition of the order 
has to be somewhat stretched, since this plant exhibits 
in many respects a striking resemblance to Litho- 
derma, and in these same points a divergence from 
Sphacelariacee. The thallus of Battcrsia consists of a 
creeping cushion of several layers of cells fixed to the 
substratum by its undersurface,and giving off upwards 
short simple or branching shoots which bear the 
sporangia terminally. These shoots consist of single 
cell-rows, though occasionally they form several 
rows at the base, after longitudinal division of the 
cells. 
Most of the Sphacelariacee spring from a basal 
cushion which grows by its marginal cells, or from a 
weft of rhizoids which penetrate the tissue of the 
