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, Rividaria. At left gelatinous mass of 

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

 • — hr, hormogonium; li, 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. 



