THALLOPHYTES 
43 
posed of eight triangular, platelike cells known as shields (fig. 115). 
Projecting centripetally from the center of each shield is an elongated 
cell (manubrium), which bears a terminal cell (head cell). These head 
cells give rise to a varying number of similar cells, and each ultimate 
cell produces a pair of long filaments, each consisting of approximately 
200 cells, each cell producing a single sperm (figs. 117, 118). The in- 
terior of the antheridium, therefore, is a tangle of filaments, and the 
115 
FIGS. 115-119. Chara: 115, branch bearing oogonium (snowing its sterile jacket 
and crown) and antheridium (showing its interlocking, shieldlike wall cells); 116, young 
oogonium (stalked and not yet completely invested by the jacket) and antheridium; 
117, manubrium bearing head cells and sperm-containing filaments; 118, detail of cells 
of filament showing contained sperms; 119, sperms (spirally coiled and biciliate). 
After SACHS. 
sperm output of a single antheridium may range between 20,000 and 
50,000. The sperm is a more specialized structure than is the zoospore- 
like sperm of the ordinary algae, and more resembles the sperms of 
higher plants. The nucleus with its sheath of cytoplasm forms the body ; 
the cytoplasm extends to form an elongated more or less spirally coiled 
beak, and from its tip two long cilia are produced (fig. 119). 
Oogonium. The oogonium, which replaces a secondary branch, is 
an enlarged apical cell, and produces a single large egg rilled with starch 
