Zygnemex 



343 



Sub-family ZYGNEMEX. The Algae included in this sub-family consist of 

 unbranched filaments of cells similar to those of the Mesocarpese, but usually 

 of slightly larger size and with much shorter cells. The cell-wall is also 

 stronger and thicker, the strongest walls occurring in Zygnema ericetorum 

 (fig. 214 C', fig. 215). Each cell possesses a centrally placed nucleus, embedded 

 in a small amount of cytoplasm (fig. 215 D and E; fig. 216 E}, and two 



Fig. 214. A, Zygnema stellinum (Vauch.) Ag., x 430. E, Z. Vaucherii Ag. var. star/mile (Hass.) 

 Kirchn., x 430. C, Z. ericetorum (Kiitz.) Hansg., x 415. D, Z. leiospermum De Bary, x 430. 

 E, Z. insigne (Hass.) Kiitz., x 330. F, Z. Ralfnii (Hass.) De Bary, x 430. ap, aplanospore. 



chloroplasts (except in Zygnema ericetorum), the latter being axile in Zygnema 

 and Pyxispora but parietal in Pleurodiscus (fig. 216 D). Each chloroplast is 

 furnished with a central pyrenoid. 



In Zygnema the two chloroplasts are generally star-shaped, having 

 numerous radiating branched processes (fig. 216 E). Z. ericetorum is a 

 notable exception in which there is but one deeply constricted chloroplast, 



