250 University of California Publications. [Botany 



those by Fischer, Kohl, Macallum, Phillips, and finally Olive's 

 ingenious tabulation of opinions. It is thought expedient, how- 

 ever, to say a few words concerning the nature of the problems, 

 and particularly concerning the recent efforts toward their so- 

 lution. 



Since the nucleus in the higher organisms is looked upon as 

 the governing center of cell activity, the demonstration of the 

 presence or absence of such an organ in the Cyanophyceae cell 

 was naturally one of the first things to claim the attention of the 

 cytologist. The first paper to appear on the subject was by 

 Schmitz in 1879. He decided that the Cyanophyceae cell has a 

 nucleus, but the next year after further investigation he changed 

 his mind. Of the thirty or more writers on the subject, about 

 one-half share Schmitz 's final opinion. 



The question of interest and importance which naturally fol- 

 lows the demonstration of a cell nucleus is the interpretation of 

 its behavior during cell division. Of the workers who find a nu- 

 cleus in the Cyanophyceae about one-half claim that its division 

 is mitotic, and the other half that it is amitotic. Thus we have a 

 series of views on this subject ranging from that of Schmitz, who 

 claims that there is no nucleus, to Lawson, who sees a primitive 

 nucleus, and Wager, who sees a nucleus with amitotic division, 

 and finally to the other extreme held by Kohl and several others, 

 who find a nucleus with mitotic division. No less confusion pre- 

 vails among workers respecting other cell-organs. 



Three papers have recently appeared describing mitosis in the 

 Cyanophyceae, but their descriptions signally fail to agree, even 

 when relating to the same species. They are by Kohl, Phillips, 

 and Olive. 



Kohl worked upon Tolypothrix lanata Wartmann, Nostoc cae- 

 ruleum Lyngbye, Anabaena catenula B. & F., Oscillatoria limosa 

 Ag., and Oscillatoria splendida Greville. His preparations re- 

 vealed to him the presence of a nucleus without a nuclear mem- 

 brane, and further that the nucleus divides mitotically. He di- 

 vides this mitotic process into six stages, viz., first, the formation 

 of a spireme ; second, the breaking of this spireme into a definite 

 number of chromosomes, which arrange themselves parallel to the 

 long axis of the cell ; third, the constriction of the mitotic figure 



