Cytology and Movements of the Cyanophycece. 335 



Plate XXV. 



Fig. 75. First stage in the formation of the heterocyst of Nostoc. 



Figs. 76-79. Successive stages in the formation of the heterocyst of 

 Nostoc. 



Figs. 80-83. Four successive steps in the formation of the net-spireme 

 and division of IVollea saccata. 



Figs. 84-86. Different steps in the formation of the spores of IVollea 

 saccata. 



Figs. 87-89. Stages in the division of Anabccna Aos aqua. The steps 

 follow the order of the letters from a to h inclusive. 



Figs. 90-92. Colonies of Gloeocapsa polydermata, showing the cell wall 

 surrounding different generations of cells. Evidently here there are 

 more laminae laid down after each division than is found in other 

 forms. 



Fig. 93- Cells of Nostoc slightly disintegrated, showing the long pro- 

 toplasmic connections between the cells. 



Fig. 94. Trichome of Spermosira litorea, showing how the sheath is 

 formed by the deposition of layers of substance on the inner face of 

 the parent walls. As division proceeds, these walls are made to 

 hold different numbers of cells, as described in the text. 



