'22 Olive, Mitolic division (jf tlio imcloi ol' 1 he ( 'j'^unopliyceae. 



sharply tlirougliout tlieir ontire leiif^tli. In citlier of tlie two 

 Standard stains, one can, however, see theiii, iisually very dimlv^ 

 defined, cxtending only a sliort distance from tlie central body. 

 A general cytoplasmic stain sonietimes gives l^etter rosnlts witli 

 tliese structiires; and, in faet, in the expericnce of the writer, 

 was actnally necessary in showing the libiils in their entire 

 lengtli. 



As lias been pointed ont above, the dense, libroiis, achromatic 

 portion of tlie dividing central body between the two groups of 

 separating chromosomes (as, for example, in fig. 8), cannot well 

 be interpreted otherwise than as the „central spindle"; and the 

 fibrils that lead from the chromosomes to the walls appear. at 

 least, to fnnction as mantle tibers. Tliere remains, therefore, in 

 presenting proofs of mitotic division, to discuss the more important 

 phenomena accompanying mitosis, viz., the iission of the ohromatin 

 graniües and their arrangement in a spireme. 



A detailed account of the mitotic division of the nuclens 

 in Gloeocapsa jfolydprmatica will be reserved tili later, since the 

 process in this species involves certain peculiarities which merit 

 a special discussion. 



Hegler (Ol) says that in Anabaena, during the division of 

 the nucleus, the minute chromatin granules fuse with one another 

 to forin a .,grösseren Verbänden, deren Ghromosomennatur an 

 günstigem Untersuchungsmaterial nach Fixieren mit sclnvefliger 

 Säure und Färbung mittels der angeführten Methoden durch ihr 

 weiteres Verhalten beim Teilungsprozess festgestellt werden 

 könnte'" (p. 352). I have never seen any such fusion of chro- 

 matin granules to form chromosomes. In fact, if normal, such a 

 process as the union of chromatin granules to form chromosomes 

 should take place early in the formation of the spireme thread. 

 I am certain that a fusion of the chromatin granules does not 

 occur in the spireme thread of Gloeocapsa, unfortunately the only 

 instance in which I can speak positively on this point. 



In the cells of Oscillatorla, we can frequently see nuclei 

 which appear to be in a spireme stage (fig. 7, the lowermost cell ; 

 flg. 10, the two middle cells; fig. 1-1, the four cells at the right; 

 fig. 17, the low^ermost cell). But particularly in cross sections, 

 do we find appearances which suggest at once a thickened 

 spireme thread, in which the achromatic and chromatic sub- 

 stances seem to be blended (figs. 25, 42). Moreover, such nuclei 

 as are shown in the two middle cells of figs. 8 and 10 probably 

 represent in section a similar condition to the spireme stage of 

 the nucleus oi Gloeocapsa seen in figs. QS^ 70, 7-1, and 75. It 

 should be kept in mind, however, that, in Gloeocapsa, the spireme 

 is in the form of a simple, more or less spiral thread; wliereas, 

 that which we see in section in the case of Oscillafona, lias its 

 convolutions disposed in a disc-shaped figure. In both instances, 

 we may see the beginnings of the longitudinal fission of the 

 spireme, resulting in the doubling of the ]iumber of chromatin 

 granules. In neither case, however, is there evident a subsequent 



