280 University of California Publications. [Botany 



VII. RESULTS. 



1. The cell of the Cyanophyceae contains a nucleus which in 

 some species is sharply delimited from the surrounding cyto- 

 plasm, while in others the differentiation is much less marked. 



2. The nucleus occupies a relatively large portion of the cell, 

 its shape being determined by the shape of the cell. In short- 

 celled filamentous species its greater diameter is across the fila- 

 ment, while in long-celled species it extends in the direction of 

 the long diameter of the cell. 



3. In all the species studied, with the possible exception of 

 Synechocystis, the nucleus divides amitotically, beginning at the 

 periphery and gradually proceeding to the center. In Synecho- 

 cystis aquatilis a primitive form of mitosis has developed, in 

 which there is a spireme formed which separates into three pieces. 

 These arrange themselves parallel to each other and to the long 

 diameter of the cell, after which they are divided crosswise, and 

 the ingrowing cell-wall completes the cell division. No longitud- 

 inal splitting of the thread occurs. 



4. The nucleus consists of granules, chromatin, and an achro- 

 matic ground substance in which the two former substances are 

 imbedded. In some forms (e.g., the large short-celled species of 

 Oscillatoria) the chromatin is disposed in the ground substance 

 in the form of disconnected masses; in others (e.g., Symploca 

 Muscorum) it is somewhat united into a coarse thread-like mass ; 

 and in still other cases (e.g., Dermocarpa) the chromatin is 

 united into a definite network. 



5. The nucleus may be induced to assume a resting condition 

 by very slow desiccation. 



6. There is no definitely organized chromatophore, the cyto- 

 plasm holding the coloring matters. 



7. Cell division is completed in the filamentous forms by the 

 gradual ingrowing of the ring-shaped cell-wall. The division of 

 the chromatin in some species seems to precede the ingrowing of 

 the cell-wall; in others it accompanies it, beginning at the out- 

 side of the mass, and keeping pace with the ingrowing wall ; and 

 in still other species the cell-wall actually grows to and against 

 the chromatin, gradually crowding it toward the center as if it 



