Cytology and Movements of the Cyanophycee. 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 Cylindrospermum 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 
