24 Olive. Mitotic di visiou of the nuclei of the Cyauophj^ceae. 



inaiii axis of tlio cell; ^vhile tlie second division is also trans- 

 verse, and results in twelve shortor daughter chromosomes. The 

 two lowermost cells of Wäger' s fig. 1 show nuclear bodies which 

 are quite similar in many respects to some from Avhicli Kolil 

 derived liis diagrams to illustrato his sclieme of mitosis; an Ob- 

 servation jDarticularly interesting from the fact that Wager 

 eoncluded from such appearances that the division of the nucleus 

 is amitotic. It has already been pointed out in this paper that, 

 in the opinion of the writer, such appcarances as are figured by 

 both Kohl and Wager are misleading, and that they have 

 probably resulted from too thick or from overstained prepara- 

 tions. Such an opinion is based upon the fact that the writer 

 lias also often obtained many similar results in mounts of Os- 

 cillatoria and other species, in which the cells were either poorly 

 fixed or in which the stain was not well differentiated, owing 

 to insufticient washing out, or to the section being too thick 

 (figs. 2 and 3). 



Division of tlie cell. 



It is Said that in Spirogyra the partition waW which grows 

 across the cell, thus cutting it in two, appears only after the 

 nuclear division is accomplished. In the Cyanopliyceae, on the 

 other hand, we apparently have the new ring-formed partitions be- 

 ginning to grow in from the outer walls long before nuclear 

 division is fully completed. The striking example has already 

 been mentioned, how in OsclUatoria princeps and 0. Froelidiia^ 

 division may take place with such wonderful rapidity that we 

 may have, in one cell at the same time, as many as three ring- 

 formed walls in different stages of growth (figs. 11, 13). In this 

 instance, long Ijefore the two daughter nuclei are completely 

 severed from each other, the daughters themselves have begun 

 to divide mitoticaUy. Wager (03) also has noted the fact that 

 several divisions may go on at the same time and he fuiiher 

 points out that the division of the cell appears to go on inde- 

 pendently of the nuclear division. Figs. 6 — 9, 14, 17, 34 show the 

 usual condition, in which the cells are completely cut in two 

 before a second division wall begins. 



Close examination further reveals the highly interesting fact 

 that in the filamentous forms, the division of the cells takes 

 place with more or less rhythmic regularity. According to Mac- 

 f arlane (Ol), a similar wave-like rhythm of division activity has 

 been observed in Spirogyra. Fig. 9 is a camera drawing of Os- 

 cillatoria Froelicliia, showing clearly this phenomenon. In this 

 figm-e, three maxima are indicated, at ö, f?, and a third at hc, 

 points at which division has progressed the farthest. Two cells 

 below a is a central body in which division is least advanced, 

 and half way between c and d is another point of minimum 

 advancement. At both h and c are cells which have completed 

 division, the two daughter cells at /; liaving apparently hnished 

 this act sooner than the two at c. In the young nuclei shown 



