No. IO.] FRESH-WATER ALG^E. 67 



Z. pectinatum (Vauch.) Ag., Fig. 279. In conjugation. 



Z. cruciatum (Vauch.) Ag., Fig. 180. 



Spirogyra Link. Cells with from one to many bands of 

 chlorophyll in the cell wall, winding to the right. The* zygo- 

 spores are always inside the walls of one of the conjugating 

 cells. 



The length and width of the cells, the form of the 

 dividing wall (which may be plane or replicate, i. e., with an 

 annular ingrowth of cellulose), the number of spirals, and the 

 number of turns each spiral makes in a cell, are all points for 

 consideration ; but the zygospores form the only decisive 

 factor in the determination of species. In the determination 

 of the species given below, we have chiefly relied on the 

 vegetative thread. 



Found in low-lying ponds and ditches. 



5\ varians (Hass.) Kutz., Figs. 181, 182. 



S. Weberi Kutz., Figs. 183, 184. 



S. maxima (Hass.) Witt., Fig. 185. 



5". jugalis (Dillw.) Kutz., Figs. 186, 187. 



5". inflata (Vauch.) Rab., Fig. 269. 



6\ calospora Cleve, Fig. 105. 



S. dubia Kutz., Fig. 188. 



5". qninina (Ag.) Kiitz., Figs. 189, 190. 



S. Grevilleana (Hass.) Kiitz., Fig. 191. 



S. majuscula Kutz., Fig. 192. 



5\ adnata Kiitz., Fig. 193. 



5\ Spreeiana Rab., Fig. 194. 



5\ decimina (Mull.) Kutz., Fig. 196. 



S. communis (Hass.) Kiitz., Fig. 197. 



S. Huviatilis Hilse, Figs. 198, 199. 



5". mirabilis Hass., Fig. 202. 



6". bellis (Hass.) Cleve, Figs. 203, 204, 270. 



5*. Havescens (Hass.) Cleve, Fig. 205. 



5\ crass a Kiitz., Fig. 60. 

 [S. nitida (Dillw.) Link.] 



Choaspis S. F. Gray (Sirogonium Kiitz.). Fila- 

 mentous. The only genus of Conjugatae without a mucous 

 coat. Sterile cells much like Spirogyra; conjugating cells 

 arise by unequal division of the cells of the filaments, and, 



