Algae. 225 



2. This nucleus divides by one of two methods, both of 

 which Start upon the kar} okinetic history, one going no further 

 than the net-spireme stage where it constricts itself into halves, 

 while the other continues further and forms a rudimentary 

 spindle with rudimentary chromosomes upon linin threads. 



3. In both forms of division, the nucleus divides itself, 

 not being strangled into two parts by the ingrowing parti- 

 tion wall. 



4. The chromatin is arranged on the spireme thread in 

 granules which multiply in number by transversa divisions. 



5. There is no longitudinal Splitting of the chromosomes 

 or of the spireme, and in the division of the cell by the me- 

 thod first mentioned above, the two portions of the nucleus are 

 not necessarily equal. 



b. The chromatin is aggregated in hollow vesicles in the 

 resting cell. These vesicles give out their chromatin to the 

 net-spireme very much like the nucleoli of higher plants, and 

 they may represent them. They are imbedded in a granulär 

 ground substance. 



7. The outer zone of the protoplast is divided into two 

 portions, a thin colorless ectoplasm lining the cell wall, and the 

 thicker layer between it and the central body. This latter 

 portion contains the pigments which are dissolved in it^ and 

 is rightfully termed the chromatophore. 



8. The cyanophycin granules and slime balls are probably 

 food products. They are located in the chromatophore. 



9. The movements of Osclllaria, Cylindrospermiim and the 

 other forms of the Cyanophyceae which exhibit motion, are 

 caused by delicate protoplasmic cilia distributed along the sides 

 of the trichome. 



10. Finger-Iike processes of the ground mass of the nucleus 

 radiate out toward the periphery of the cell, piercing the chro- 

 matophore and ceii vv^ai!, and project in the form of the cilia 

 which cause the movements of the trichomes. 



11. The finger-like processes upon the end cells of Oscll- 

 laria, and those surrounding the heterocysts and spores of 

 Cylindrospermiim, are not parasitic, but definite organs of the 

 cell, having a motion of their own. They apparently assist the 

 trichomes to pass around obstacles. 



12. The protopiasts of the cells of filamentous Cyanophy- 

 ceae are all connected by fine protoplasmic threads which pass 

 through communicating pores in the w^alls. There is usually 

 one central pore, though other finer pores and threads may 

 be present. 



13. The heterocyst is a modified vegetative cell which 

 gradually fills with some substance, passed to it from the other 

 cells, through the pores for the protoplasmic threads which 

 connect it with the other cells of the trichome. This substance 

 finally fills the whole of the heterocyst. It gives some of the 



Botan. Centralblatt. Bd. XCVIII. 1905. 15 



