THE THALLOPHYT ES 343 
tion is accomplished either asexually by fission or sexually by 
‘ conjugation. 
FamiLy ZYGNEMACE&.—This is a family of pond scums includ- 
ing the well-known genera, Spirogyra and Zygnema [Fig. 245 (11, 
. 13)]. 
Fic. 248.—Spirogyra sp. A, terminal portion of vegetative filament; B, stages 
of scalariform conjugation; C, preparation for lateral conjugation; D, zygospores 
formed by lateral conjugation. (Gager.) 
Spirogyra or Brooksilk is a filamentous organism found sus- 
pended or floating in masses in quiet water. Each filament, 
when examined microscopically, will be found to consist of more 
or less elongated cylindrical cells arranged end to end, the ter- 
minal cells having rounded extremities. Each cell has a cell wall 
