452 THE AMERICAN NATURALIST. [Vol. XXXVIII. 



But the essential characteristics of kinoplasm stand out sharply 

 from whatever point the phenomena of mitosis is viewed, and in 

 this protoplasm with its power of forming contractile fibers is 

 vested some of the most conspicuous activities of nuclear division 

 as well as the important powers given plasma membranes in 

 relation to the segmentation of protoplasm to be considered 

 presently. ' ' 



The dynamic activities concerned with the spindle present only 

 half the story of mitosis. The other important events occur 

 inside of the nucleus. One of these is the dissolution of a por- 

 tion or the whole of the nucleolus which takes place as the 

 spindle develops and we have already given the views of Stras- 

 burger ('95 and : 00), supported by the studies of other investi- 

 gators, that its substance in certain instances furnishes material 

 for the development of the spindle. But the chief events in the 

 interior of the nucleus deal with the accumulation of chromatin 

 on the spirem thread which with the disappearance of the linin 

 indicates that the latter substance may become converted into 

 the former. The splitting of the spirem ribbon longitudinally is 

 of the utmost significance for thereby is made possible an exact 

 and homogeneous distribution of the chromatic material in the 

 nucleus. We do not know how the spirem ribbon splits nor 

 have we as yet any evidence of the origin and evolution of this 

 peculiar activity. 



(b) Segmentation of the Protoplasm. 



Mitosis in the uninucleate cells of plants is generally followed 

 by immediate cell division, which takes place in groups above 

 the thallophytes through the formation and cleavage of the cell 

 plate in the equatorial region of the spindle between the daughter 

 nuclei. Among thallophytes, as so far studied, cell division is 

 chiefly through cleavage by constriction. There are forms among 

 the thallophytes and also in the spermatophytes whose nuclei 

 gather about themselves a portion of the cytoplasm, wherein 

 they lie, which becomes cut out of the general mass by a cell 

 wall. This is free cell formation. 



Multinucleate masses of protoplasm, such as plasmodia and 



