HOW TO KNOW THE FRESH-WATER ALGAE 



143a (141) Cells cylindrical, 10 or more times the diameter in length, 

 the poles truncate; wall spiny. Fig. 107 GONATOZYGON 



Fig. 10 7. Gonatozygon 

 .. i l acuieafum Hastings. 

 ftUJ^ This desmid-like genus 



" ViiWvW H V^ haS solitar Y cells whic ; h 



' are nearly always a little 



Figure 107 crooked; have walls bear- 



ing long or short spines; 

 are not constricted at the midregion. Although usually free-floating 

 and intermingled with desmids, the cells may be adherent to sub- 

 merged plants. There is a ribbon-like chloroplast that is axial rather 

 than parietal. As mentioned above, Gonatozygon may be classified 

 with Genicularia to form the Gonatozygonaceae by some authorities, 

 whereas others place it with the saccoderm desmids in the family 

 Mesotaeniaceae. 

 143b Cells fusiform short-cylindric, less than 10 times the diameter 



in length; wall smooth 144 



144a Cells broadly fusiform or subcylindrical; 2 chloroplasts, one in 

 each end of the cell, bearing longitudinal ridges, usually with 

 notched margins. Fig. 108 NETRIUM 



fe«eW&?^ 









mL 



Figure 108 



Fig. 108. Netrium digitus (Ehr.) Its. & Rothe. 



These are "watermelon"- or "cucumber"-shaped cells which are sac- 

 coderm desmids with scarcely any or no constriction in the midregion. 

 Like other members of the family the cell contents are conspicuously 

 symmetrically divided into two portions, there being 1 (rarely more) 

 longitudinally ridged chloroplasts in each half of the cell. There are 

 5 or 6 species in this country, differentiated by shape and proportions 

 of the cell. 



144b Cells cylindrical or narrowly fusiform, with 1 chloroplast in the 

 cell 145 



145a Cells "cigar"-shaped; chloroplast axial with 4-6 pyrenoids. Fig. 



109 ROY A 



Fig. 109. floya obtusa (Breb.) 



r"- 1 '-!--?.-.-:.- " — | 



ft & . % q- . ;*p^ 



m 



West & West. 

 This rather rare saccoderm 

 desmid has slightly curved 

 Figure 109 cylindrical cells in which 



there is but a single chloro- 

 plast that is notched in the midregion where the nucleus is located. 



73 



