Vol. 2] Gardner. — Cytological Studies in Cyanophyceae. 253 



Relative to the splitting of the chromosomes, his eighth con- 

 clusion reads: "Finally, the most necessary requirement of 

 mitosis is fulfilled in that a longitudinal fission of the chromo- 

 somes occurs. This is plainly evident in the case of Gloeocapsa, 

 in which the simple spireme threads divide lengthwise, begin- 

 ning at the two ends and splitting thence progressively to the 

 middle of the thread. It) is highly probable, further, that the 

 splitting of the convoluted spireme of the filamentous species 

 takes place in a somewhat similar manner, since the fission plane 

 begins at the edge of the disc-shaped figure and travels progres- 

 sively inward to the middle. ' ' 



Finally I wish to quote his eleventh conclusion concerning the 

 continuity of mitotic activity. 



"Although the central body in vegetative filaments seems to 

 be in a continuous state of mitotic activity, it appears occasion- 

 ally to make a beginning toward a resting condition and to form 

 a delicate membrane and karyolymph. It is probable, however, 

 that the nuclei in the active filaments do not ordinarily approach 

 nearer to a state of rest than the spireme condition or a stage 

 immediately prior to it. ' ' 



From the foregoing it will be seen that these three authors all 

 agree that there is a nucleus in the Cyanophyceae. They have all 

 worked upon at least one species in common, Oscillatoria limosa 

 Agardh (0. Froelichii Kiitzing), yet they have three different 

 interpretations as to the manner in which this nucleus divides. 

 Of these three, Olive seems to have found the greatest conformity 

 in nearly all particulars to the various steps in the typical mitosis 

 of a higher plant cell. 



After very careful and prolonged investigation I am unable 

 to subscribe to any of the conclusions just quoted concerning the 

 mitosis of the nucleus in any of the Cyanophyceae upon which 

 they have worked. I have carefully investigated Oscillatoria 

 limosa and 0. splendida, two species upon which Kohl worked, 

 and can speak positively in regard to mitosis in these. There is 

 in no portion of the life-history of the cell any configuration of 

 the chromatin present that can be interpreted as belonging to a 

 mitotic process. The process in the nuclei of these two plants is 

 purely and simply amitotic. Kohl's conclusions are based pri- 



