DESMIDS, DIATOMS, AND FRESH-WATER ALGjE. I03 



Fig. 82, — Batrachosperraum 

 monilif6rme. 



beaded. The whorls of branches are often so close to- 

 gether that the entire plant, 

 as it floats beneath the water, 

 seems to be a string of little 

 balls. Under the microscope 

 each moniliform thread is usu- 

 ally seen to be terminated by 

 a colorless hair-like bristle. 

 This, however, it not always 

 present. With a high power 

 the ends of the beaded fila- 

 ments may be seen to run 

 down the main stem in long, 

 narrow, almost colorless cells. B. monilifdrMe, Fig. 82. 



2. Anab^na (Fig. 83). 

 Filaments moniliform, freely floating, the cells 

 spherical, the larger scattered ones globular, yellowish. 

 The filaments are often 

 curved, and sometimes 

 surrounded by a delicate 

 gelatinous material, in 

 which the filaments are 

 often collected together 

 in a mass. There are 

 several species, all of 



which closely resemble each other (Fig. 83). They 

 are supposed to be a stage in the development of 

 some othei- algse. Similar filaments, but with a gela- 

 tinous sheath, belong to the genus Nostoc. 



3. OscillAria (Fig. 84). 

 • These plants are found almost everywhere in stand- 

 ing water. They often form thick floating mats of a 



Fig. 83. — Anabaena. 



