DEVELOPMENT OF PLANTS 



147 



manently retain their power of motion. No cilia have been ob- 

 served for a certainty in any of these forms and the cause of 

 the motion has been ascribed to the interchange of fluids attend- 



m 



Fig. 93- 



Fig. 92. Forms of the Cyanophyceae : A, Glcocapsa. 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 

 gelatinous, spherical masses of the plants as they appear floating upon the 

 surface 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, Rivularia. At left gelatinous 

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

 plants enlarged — hr, hormogonium; h, heterocyst. 



Fig. 93. One of the most common forms of the Cyanophyceae, Oscil- 

 latoria. 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. 



