104 FRESH-WATER BIOLOGY 



A few of the Cyanophyceae show remarkable oscillating, gliding, 

 or rotating movements, the cause of which has never been satisfac- 

 torily explained. In Oscillatoria and Spirulina, these movements 

 are particularly conspicuous. 



CYANOPHYCEAE 



(myxophyceae, phycochromophyceae, schezophyceae) 



Algae possessing more or less of a blue-green color; free-floating or living in 

 gelatinous masses or strata; sexual reproduction unknown, reproducing asexu- 

 ally by means of cell division, the daughter cells either soon separating into 

 more or less independent cells, or remaining adherent to form filaments or 

 plates or solid colonies. The vegetative cells each made up of two more or 

 less easily distinguishable parts: a colored peripheral cytoplasm, which contains 

 the bluish or reddish phycocyanin, in addition to the chlorophyll pigment, and 

 also generally a number of minute granular bodies — the "cyanophycin gran- 

 ules"; and the colorless "central body," which is the nucleus of the cell. 

 Embedded in the central body, in addition to the chromatic and achromatic 

 substances, there usually occur a few large, globular, transparent bodies — 

 the so-called "slime globules." Sap vacuoles sometimes occur in the cyto- 

 plasm. Thick-walled resting spores are formed in some species; heterocysts 

 are also found in certain forms, which are peculiar cells, whose protoplasmic 

 contents apparently soon die and whose significance is but little understood. 



1 (25) One-celled plants, Hving either free or united into colonies by 



being embedded in a common gelatinous matrix. 



Order Coccogoneae Thuret . . z 



2 (24) Cells generally free-floating or forming a gelatinous stratum; not 



differentiated into base and apex. 



Family Chroococcaceae . . 3 



3 (8, 11) Cell division in one plane only 4 



4 (7) With wide mucous covering . . . . S 



5 (6) Cells elongate, each with a special mucous coat. Gloeothece NageU. 



Cells oblong or cylindrical, with thick, sometimes lamel- 

 lose, gelatinous membrane; single or united into micro- 

 scopically small colonies, which are enclosed after the 

 manner of Gloeocapsa within the gelatinous membrane of 

 the mother cell. On wet rocks, rarely floating. 



Fig. 32. Gloeothece conflums Nageli. X 450. (After West.) 



6 (5) Cells httle longer than broad, many adhering together to form 



large, irregular colonies, enclosed by a common mucous 

 matrix Aphamthece Nageli. 



Cells oblong, dividing only at right angles to the long 

 ams; forming irregular, gelatinous colonies which some- 

 times grow to be an inch or more in diameter. At 

 margins of lakes and on wet rocks. 



Fig. 33. AphatMthKemkroscDpka'iiiifii. X 1000. (Original.) 



