Cytology and Movemeyits of the Cyanophycecz. 305 



tin being passed into it through the communicating pore 

 from the other cells of the trichome. This passage of chro- 

 matin is quite evident from the appearances of the cells and 

 the behavior of the spores. The end cell then divides, and 

 the sister cells thus formed grow apart about one quarter 

 the distance of the short diameter of each cell, though both 

 still retain a strong protoplasmic connection. Part of the 

 jelly-like sheath of the trichome masses itself around these 

 cells as they begin to grow ; the short cilia that were found 

 upon them when they were vegetative cells now elongate 

 into strong hair-like flexible processes, passing from the pro- 

 toplasts of both cells through the cell walls. The protoplasm 

 of the outer or end cell becomes granular, and its chromatin 

 diffused. It soon ceases to grow and becomes the hetero- 

 cyst. The sister cell, being in contact with the other cells 

 of the trichome, can draw upon them for nourishment 

 through the intercellular pores. It grows greatly (Fig. 59), 

 the chromatin remaining in the vesicles as in the vegetative 

 cells, but here the cells are much more abundant and multi- 

 ply by division until they fill nearly the whole lumen of the 

 cell (Figs. 55, 57, 60). After the spore has grown to the 

 full size, it withdraws its hair-like processes, forms a thick 

 laminated wall around itself and becomes dark brown from 

 the deposition of pigment (Figs. 61 and 62). The hetero- 

 cyst later loses its hair-like appendages, and the organism 

 settles down into the resting stage. The cells all disinte- 

 grate, except the resting spore and the heterocyst, which 

 remain intact and connected for a long period of time, the 

 heterocyst being filled with food substance in the form of 

 cyanophycin. In Cylindrospermiim the heterocyst cell is 

 usually the terminal cell of a filament. It merely has the 

 nutriment which was formed within itself, or that passed 

 into it before it separated from the spore cell. But if the 

 organism be grown in a full nutrient solution, or if the cell 

 which divided to form the original spore and heterocyst be 

 in the middle of the trichome as is sometimes, though not 



