No. 466.] STUDIES ON PLANT CELL VIIL 697 



Olive (: 04) has given especial attention to methods of sec- 

 tioning and staining on the slide and presents the most detailed 

 account of the structure and behavior of the chromatin and the 

 simple apparatus which brings about the division of the central 

 body. The central body is made up chiefly of dense kinoplasm 

 with a fibrillar structure in which lie chromosomes that may be 

 counted and whose number is found to be constant in several 

 species. Thus there are eight chromosomes in a species of 

 Gloeocapsa and Nostoc and sixteen in certain forms of Oscilla- 

 toria, Phormidium, and Calothrix. The chromatin in some 

 cases was observed to be organized into what seemed to be a 

 simple type of spirem (especially clear in Gloeocapsa) within the 

 central body, and the chromosomes are formed by a concentra- 

 tion of material at certain points which are constant in the cells 

 of the same plant. 



Olive found evidence that the chromosomes split during the 

 process of division of the central body and are gathered in two 

 groups at the ends of the achromatic structure which is gener- 

 ally flattened at the poles and conforms in other particulars to 

 the shape of the cells. The two sets of chromosomes are 

 finally separated by the cell wall which develops from the pe- 

 riphery during cell division and cuts the achromatic structure 

 in the middle region. That portion of th? central body which 

 remains between the two sets of daughter chromosomes is 

 regarded by Olive as equivalent to the . central spindle so well 

 defined in stages of anaphase and telophase in mitoses of higher 

 plants. The central body during this process of division has 

 certainly very much the appearance of a simple type of spindle 

 although there are not present the large fibers so characteristic 

 of nuclear figures in higher plants. Moreover it can scarcely 

 be held that the division is one of simple fusion when chromo- 

 somes are present in constant numbers and split into two groups 

 with each division of the cell. Olive believes that the achro- 

 matic structure, present during cell division, is a disc-shaped, 

 generally flat-poled spindle, densely fibrous in structure and that 

 the fission of the chromosomes and their separation into two 

 sets constitutes a true mitotic division of the central body, which 

 is a nucleus. 



