166 REPRODUCTION OF THE CYANOPHYCEAE 



sion, as in the case of the bacteria, many of the thread-like forms 

 have another interesting method of increasing their numbers. 

 A few of the cells, termed a hormogonium, become separated 



FIG. 92. FIG. 93. 



FIG. 92. Forms of the Cyanophyceae : A, Gleocapsa. At the right a cell 

 has divided, but the two daughter cells are held together in a gelatinous 

 mass. Above numerous divisions have occurred, but all the cells are sur- 

 rounded by a mucilaginous envelope. B, Nostoc. Below appear the gelat- 

 inous, spherical masses of the plants as they appear floating upon the sur- 

 face or resting on the bottom of ponds. At the right a plant enlarged 

 h, heterocyst; s, thick- walled resting cells or spores. At the left a spore has 

 germinated, producing five cells. C, Rivnlaria. At left gelatinous mass of 

 plants attached to stem of water plant. At right view of a few of the plants 

 fir, hormogonium; h, heterocyst. 



FIG. 93. One of the most common forms of the Cyanophyceae, Oscillatoria. 

 The different sizes of the cells show that cell division may occur in any of 

 the cells of the filament e, a decaying cell which will ultimately free the 

 cells below it as a hormogonium. 



