Vol. 2] Gardner. — Cytological Studies in Cyanophyceae. 255 



the chromatin arrives at a place of variability. There are either 

 several fine chromosomes, or the segments may consolidate into a 

 few large chromosomes. The next step is the simultaneous cross- 

 division of these parallel chromosomes in the middle. The cell- 

 wall grows across and completes the division by cutting in two 

 the "linin connectives," and forming the two daughter cells. 

 The fate of the daughter chromosomes is here again uncertain. 

 They are either resolved into a new network or changed back 

 again to the chromatin vesicles. 



It is to be noted in this scheme of mitosis that extreme varia- 

 bility prevails. 



The karyokinetic process as described by Olive is here briefly 

 outlined. 



Chromatin granules are embedded in the achromatic substance 

 of the never resting cell. These granules arrange themselves 

 along a linin thread, which becomes the "segmented spireme" 

 in Gloeocapsa or the "convoluted spireme" in the filamentous 

 forms. The granules of which the spireme thread is composed 

 constitute the chromosomes of which there is a definite number 

 in the cell of each species. The next step after the formation of 

 the spireme is its longitudinal splitting, thus accomplishing the 

 equal division of all the hereditary qualities. The mantle fibers 

 extending to the cross-walls attach themselves to each dividing 

 daughter granule or chromosome, and the whole mass is pulled 

 into the daughter cell, after which the remainder of cell division 

 is accomplished by the ingrowing of the cell-wall, and separation 

 of central spindle and cytoplasm. The daughter granules, or 

 chromosomes, are still embedded within the achromatic sub- 

 stance, and a second division proceeds exactly as before. This 

 second division may begin before the first one is completed, and 

 even a third and a fourth division may be in progress before the 

 original one is accomplished. 



From these brief summaries it will be noticed that there are 

 widely different views, not only as to the number of different 

 steps involved in the mitotic process, but also as regards the es- 

 sential manner in which these processes are carried out. A clearer 

 comparative understanding of the three processes of mitosis just 

 briefly outlined may be obtained from the following treatment of 



