Filamentous Conjugates 



119 



Cosmarium (fig. 40 s). The 

 most bizarre forms are found 

 in the genera Micrasterias (figs. 

 40 q and r) and Staurastrum. 

 These connect in form 

 through Euastrum (fig. 40 o) 

 Tetmemorus (fig. 40 n) Netrium 

 (fig. 40 d), etc., with the sim- 

 pler forms which have little 

 differentiation of the poles of 

 the cell; and these, especially 

 Spirotaenia (fig. 40 b) and Gon- 

 atozygon (fig. 40 a) connect 

 with the filamentous forms 

 next to be discussed. 



The Filamentous Conjugates 

 This is the group of fila- 

 mentous algae most closely 

 allied with the desmids. It 

 includes three common genera 

 (fig. 41) Spirpgyra, Zygnema, 

 and Mougeotia. The first of these being one of 

 the most widely used of biological " types" is known 

 to almost every laboratory student. Its long, green, 

 unbranched, slippery filaments are easily recognized 

 among all the other greenery of the water by their 

 beautiful spirally -wound bands of chlorophyl. The 

 other common genera have also distinctive chlorophyl 

 arrangement. Zygnema has a pair of more or less 

 star-shaped green masses in each cell, one on either side 

 of the central nucleus. In Mougeotia the chlorophyl 



FIG. 41. Filamentous con- 

 jugates. 



a. Spirogyra; b, flat view, and c, 

 edgewise view of the chlorophyl 

 plate in cells of Mougeotia,' d, 

 Zygnema. 



a, a little more than two cells g Docidium baculum 



from a filament of Gonatozygon h Docidium undulatum 



b Spirotcenia i Closterium pronum 



c Mesolcenium j Closterium rostratum 



d Netrium k Closterium moniliferum 



e Cylindrocystis I Closterium ehrenbergi 



f Penium m Pleurotcenium 



n Tetmemorus 



o Euastrum didelta 



p Euastrum verrucosum 



q Micrasterias oscitans 



r Micrasterias americana; (for 



a third species see page 53). 

 s Cosmarium, face view, and 



outline as seen from the side 



