158 McComb : Development of the Karyokinetic 



In regard to the presence of centrosomes or centrospheres as 

 claimed by Guignard and Schaffner ('98), I must assert with all 

 emphasis that no such organs exist in the root-tip of Allium. In 

 view of the development of the spindle through a multipolar 

 structure as discovered by Belajeff ('94) and confirmed by other 

 observers, and in the presence of well-fixed and well-stained 

 preparations which show every step in the process it seems well- 

 nigh incredible that any one should be able at the present day to 

 read centrosomes or centrospheres into the process. 



In view of the foregoing observations it is quite clear that the 

 process of spindle formation in vegetative cells of the higher plants 

 is not essentially different from that observed in reproductive cells 

 of those plants. In both cases the spindle fibers, or at least the 

 vast majority of them, are of cytoplasmic origin. They may either 

 appear at first in the form of a weft about the nucleus or radiate 

 from it. It matters little or nothing whether they radiate uniformly 

 from the entire surface of the nucleus or are confined to two 

 opposite sides. In the vegetative cells in question the spindle 

 anlage may be monoaxial and strictly bipolar from the first, but 

 it is often multipolar. 



Whether the anlage be multipolar and polyaxial or multipolar 

 and monoaxial seems to be of little importance. The spindle in 

 all phases of its development is a product of the kinoplasmic fibers 

 without the intervention or instrumentality of individualized kinetic 

 centers such as centrospheres or centrosomes. 



This work was carried out in the botanical laboratories of 

 Indiana University under the direction of Prof. D. M. Mottier who 



so kindly gave me the benefit of his larger experience in similar in- 



vestigations both in the making of preparations and in the inter- 

 pretation of results. 



Explanation of Figures 24 and 25 



All figures drawn from microtome sections by the aid of a camera lucid a and 

 Bausch and Lomb y 1 ^ oil immersion and oculars one inch and two inch. 



All figures refer to Allium cepa. 



Fig. 1. A cell in which a very delicate weft of kinoplasmic fibers appear about 

 the nucleus. Chromatin thread is not segmented into chromosomes ; the free ends in- 

 dicate where the spirem was cut by the knife. 



FlG. 2. The weft of kinoplasmic fibers is removed some distance from the nuclear 

 membrane on two opposite sides, thus forming a colorless space between it and the 

 nucleus. The fibers of the weft diverge on the right and left toward the cell wall. 



