PH^EOPHYCE.E 111 



SPHACELARIACE.E. 



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 by gemmae 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 

 Sphacelariaccw. The thallus of Battersia 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 SphacclariacecK spring from a basal 

 cushion which grows by its marginal cells, or from a 

 weft of rhizoids which penetrate the tissue of the 



