OTHER MODES OF NUCLEAR DIVISION 



203 



According to Hegler (1901) the nucleus contains granules of chromatin 

 but no nucleolus or nuclear membrane, division occurring by a simple 

 form of mitosis. The coloring matter exists in the form of minute 

 granules or cyanoplasts. Two other kinds of bodies are also present: 

 albuminous slime globules and albuminous crystals (cyanophycin granules) 

 representing reserve food. 



Kohl's (1904) description of the cell of Tolypothrix (Fig. 70) is one of 

 the most detailed which has been given in this group of researches. Kohl 

 shows that the nucleus of this form has extensions reaching outward 



FIG. 70. Structure and division of the cell of Tolypothrix lanata. 

 A, cell in the vegetative state: c, cytoplasm; n, nucleus; /, fat droplets; p, phycocyanin 

 and chlorophyll granules; s, slime globules; g, granules of cyanophycin. B, four stages of 

 cell-division in Tolypothrix, showing transverse division of chromosomes. C, diagram 

 showing 6 stages of cell-division. (After Kohl, 1903.) 



toward the cell wall, and that they are withdrawn at the time of nuclear 

 division. The nucleus, which contains chromatin, also includes a num- 

 ber of large Zentralkorner, or slime globules, while in the cytoplasm are 

 fat droplets, cyanophycin granules of reserve albumen, and granules of 

 chlorophyll and phycocyanin. The nucleus, which is very rarely in the 

 resting state, divides as follows : the chromatic material forms a spireme 

 which segments into a definite number of chromosomes; these lie in the 

 direction of the long axis of the cell and break transversely as the separat- 

 ing wall grows inward from the periphery. Their halves are thus in- 

 cluded in the two daughter cells, where they form daughter nuclei without 

 membranes. 



