HOW TO KNOW THE FRESH-WATER ALGAE 



447a Individual cell sheath distinct. Fig. 325 GLOEOTHECE 



Fig. 325. Gloeofhece linearis Naeg. 



In this genus the cells are elongate 

 cylinders or bacilliform in shape and 

 are inclosed by individual sheaths all 

 within a common mucilage. There are 

 several species differentiated mostly by 

 cell shape and size. Species should be 

 compared with Aphanothece (Fig. 327). 



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m 



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Figure 325 



447b Indivi4ual cell sheath not apparent. Fig. 326 ... RHABDODERMA 



Figure 326 



Fig. 326. Rhabdodeima lineare 



Schm. & Lauterb. 



In this genus the cells are 

 elongate and cylindrical, even 

 vermiform and are much like 

 Gioeofhece except that there is no 

 individual cell sheath. The plants 

 occur in small colonies of 4, 8, or 

 16 in the plankton of lakes; is 

 sometimes in the tychoplankton. 



448a (442) Cells arranged at the periphery of a gelatinous matrix. See 

 Fig. 319 .COELOSPHAER1UM 



448b Cells irregularly scattered throughout the colonial mucilage . . . 449 



449a Individual cell sheath not distinct. Fig. 327 APHANOTHECE 



Fig. 327. Aphanothece Castagnei 

 (Breb.) Rab. 



Cells are elongate cylinders or 

 bacilliform, occurring in large co- 

 lonies up to 5 cm. in diameter and 

 .have no individual sheaths. The 

 colonies develop on the bottom 

 of lakes but become free-floating 

 and are often washed into shallow water along shore where they may 

 form a 'soupy' mass of brownish or olive-green (rarely bluish) bodies. 

 Macroscopically they appear much like Nostoc colonies (Fig.. 300) espe- 

 cially if the colonies are young and smooth in outline. 



449b Individual cell sheath distinct. See Fig. 325 GLOEOTHECE 



185 



