204 



INTRODUCTION TO CYTOLOGY 



Fig. 71. — Nuclear division 

 in Oscillatoria Froelichia. 1, 2, 

 3, 4, four successive stages. 

 {After Olive, 1904.) j 



Olive (1904) x finds that the nucleus of Oscillatoria (Fig. 71) consists 

 of a fibrous achromatic framework with a number of very small chroma- 

 tin granules, and is nearly always in some stage of division. A spireme 

 is formed carrying 16 chromatin granules (8 in Glceocapsa and 32 in one 

 species of Oscillatoria) , each representing a chromosome. The spireme 

 and its chromatin granules are split longitudinally, and the daughter 

 spiremes with the daughter granules separate, a distinct central spindle 

 extending between them. The dividing wall is formed as a centripetally 



growing partition. In Glceocapsa the cell di- 

 vides by simple constriction. The vegetative 

 nuclei of Oscillatoria very rarely approach 

 the resting condition, but in spores and 

 heterocysts they soon pass into this state, a 

 nuclear membrane and vacuole being de- 

 veloped. In the heterocyst the protoplast 

 disorganizes. Olive regards the central body 

 of the Cyanophycese as not essentially different 

 from the nucleus of the higher plants, although 

 it is relatively primitive in several features. 

 In the cytoplasm he finds both cyanophycin 

 granules and slime globules, but no cyano- 

 plasts, the coloring matters being diffused in the peripheral portion 

 of the protoplast. 



Fischer (1905), in reply to the claims of Kohl and Olive, reasserted 

 his view that the central body is not a nucleus, but rather an accumulation 

 of carbohydrate materials. The glycogen formed as a result of assimila- 

 tory activity gathers in the central body where it is transformed into 

 another carbohydrate, anabcenin, which assumes the form of sausage- 

 shaped structures. At the time of cell-division these masses of reserve 

 material are distributed by a process of "pseudomitosis" to the daughter 

 cells. Fischer therefore regards the mitotic figures observed by others 

 as significant in connection with nutrition rather than with the functions 

 usually attributed to nuclei. 



Gardner (1906), investigating a number of species, found nuclei of 

 three kinds, which he called the diffuse type, the net karyosome type, 

 and the primitive mitosis type respectively. The " diffuse type" of 

 nucleus, which has no very definite delimitation from the peripheral 

 portion of the protoplast, contains an indefinite number of chromatin 

 masses. As the cell divides this central aggregation of chromatic material 

 divides into approximately equal portions. In the "net karyosome" 

 type, found in Dermocarpa, the distinction between the nucleus and the 

 surrounding cytoplasm is much clearer. The nucleus has an achromatic 



1 A very convenient tabulation of the results of researches on cell structure in the 

 Cyanophycese up to 1904 is given by Olive. 



