CENTRAL BODY IN PHYLLACTINIA. 55 



facts seem adequately accounted for by the conception that the central 

 body is a more permanent cell element composed of the same kino- 

 plasmic material which is found in the polar rays and spindle fibers. 



I am of the opinion that the various activities shown in spindle 

 formation and the movement of the chromosomes, as well as in free cell 

 formation, are to be regarded as functions of the individual contractile 

 kinoplasmic fibrillae of the spindle and asters rather than of the centers 

 in which these fibers meet and are combined. The determination of a 

 constant fibrous connection between the central body and the chromo- 

 somes is a strong point against the so-called dynamic theories of the 

 centrosome. In such a system we have no need for the assumption of 

 any radially working force which goes out from the sphere as a dynamic 

 center. The motions of all the bodies connected with the center are 

 much more adequately provided for by the assumption of contractility 

 in the kinoplasmic fibers which connect them to the center. This con- 

 tractility is to be compared to that of the cilia and the elements of the 

 muscle cell. The comparison of the kinoplasmic fibers to cilia or muscle 

 elements suggests further that the fibers need not necessarily be arranged 

 in centered systems, and indeed we have abundant evidence in the higher 

 plants that the kinoplasmic fibers may perform their characteristic func- 

 tions in nuclear and cell division without the presence of a central body. 

 Under this conception of the central body, the types of spindle forma- 

 tion in the vascular plants on the one hand and in the fungi and algae 

 and the animals on the other can be brought together. 



The conception of a unipolar structure of the resting nucleus 

 plainly can not apply to the nuclei of the higher plants, whose spindles 

 are formed from a perinuclear weft of fibers. Still, it is by no means 

 impossible that a permanent connection between the chromatin elements 

 and the surrounding material of the cytoplasm by kinoplasmic fibrillee 

 exists also in these cases. There is considerable evidence in the pro- 

 phases of division in the pollen mother cells of the larch, as shown by 

 Allen (i), that the fibers of the cytoplasm which later form the spindle 

 are connected through the nuclear membrane with the chromosomes. 

 The difficulty in understanding how the daughter chromosomes in turn 

 become attached to fibers from one pole only of the spindle, unless the 

 chromosomes occupy definite regions in the nucleus and are perma- 

 nently attached to the kinoplasmic fibers, is just as great here as in the 

 case of the formation of the spindle in animal cells. Still, Strasburger 

 (89) holds that in the vegetative divisions in various root tips the 

 nuclear membrane disappears at the poles and the spindle fibers grow 



