18 () I i \ c, Mitotic division of tlie uuclei of ilic Cyanophyceae. 



ügs. '2, 3, 11, 13, 77 — 79. It will be seen by contrasting figs. 8 

 and 10, e. g. , witli ligs. 11 — 13, tliat tlie central body in the 

 former drawings is made up botli of deeply staining cliromatin 

 substance, and of an achromatic portion; whereas, in the lalter 

 pieparations, no such differentiation is clearly visi1)le. Especially 

 in figs. 11, 12, and 13, which are from slides colored with 

 methylene bliie, iron haematoxylin, and Flemniing's triple stain 

 respectively. the dense central body appears to be homogeneou.s, 

 as is claimed by Palla. These preparations were simply over- 

 stained and not sufficiently washed out. The same is true of 

 hgs. 2 and 3, with the difference that the washing out of tlu^ 

 stain has been carried on a step further, so that a portion only 

 of the achromatic substance remains deeply stained. This results 

 in dark streaks of chromatin and achromatin, which may some- 

 times give the appearance of long chromosomes, such as are 

 figured by Kohl and Wager. 



In all the forms studied by the writer, including species of 

 O.scillaforia^ PJwrmidium , Calothrix, Nosioc, Gloporap.sa and Cy- 

 l'indrospermum . botli chromatin and achromatin could be made 

 out in the central body, in propedy differentiated preparations. 

 Two striking pecnliarities were at once noted. First, that the 

 achromatic portion appeared to be offen made up of an unu- 

 sually dense substance; and, secondly, that the chromatin gra- 

 nules seemed relatively very minute. Particularly in CyJhidro- 

 spermimi were these pecnliarities noticable, for it could not be 

 determined, even with the highest available magnification, tlutt 

 the achromatic portion was made up of fibrous protoplasm, as 

 could be demonstrated in nearly all the other cases ; and further, 

 the chromatin granulös were so minute that they long escaped 

 detection (tigs. 80, 82—85, 89, 90j. 



The extreme density of this kinoplasmic, fibrous mass (caUed 

 by Palla ;,rüllsubstanz"), which makes up the bulk of the cen- 

 tral body, is probably mainly responsible for the inability of the 

 majority of investigators to detect the cliromatin granules en- 

 closed within it. Particularly in cross - sections of the actively 

 dividing nuclei of Oscillatoria pyinceps and 0. FroeJlcliia can the 

 fibrous nature as well as the density of the achromatin, after 

 careful examination, be made out (note, e. g., the mass in the 

 middle of fig. 18). It will be further seen that, in the longi- 

 tudinal sections (figs, 10 and 11), the density of the kinoplasm 

 varies, although, in this view, its fibrous nature is not so easily 

 demonstrable. 



In all the forms studied, with the one exception of Cylindro- 

 spermum^ the writer has discovered that the number of the mi- 

 nute chromatin granules is constant for the same species. The 

 fact that, in Cyllndrospermum ^ the cells are comparatively long 

 may have prevented me finding a cross -section in which the 

 chromosomes, as I have called them, were grouped favorably for 

 counting. For example, in some cross sections, as few as four 

 can be counted, in others, six, or even ten by focussing up and 



