456 McComb : Development of the Karyokinetic 



Another interesting phenomenon is presented in Figs. 5, 9, and 

 10. Here the chromatin spirem remains unsegmented at a much 

 later period. In Fig. 5 the spindle anlage is a monoaxial bipolar 

 structure, while the chromatin thread remains in the form of a 

 continuous spirem. The same seems to be true also in Fig. 10, 

 but here the nuclear membrane has disappeared and the spindle 

 has reached a later stage in development. (The free ends shown 



■ 



in the drawing represents part of the spirem cut by the knife in 

 sectioning.) The nucleolus is still present. In Fig. 9 the spirem 

 is partly segmented. The chromosomes when in the equatorial 

 plate are either straight rods or bent somewhat u or j -shaped. 

 They are attached to the spindle fibers either at the ends or at the 

 point of bending. Their evolution during metakinesis and the 

 anaphase are so well known that a repetition here would be with- 



out value. 



Although the spindle fibers may not in some cases be united 

 into a common point or pole when the spindle is mature (Fig. 



12), yet the several points or poles into which portions of the 



spindle fibers converge almost invariably unite into a single pole 



sometime during the anaphase. 



Fig. 13 is a typical karyokinetic figure during the anaphase. 



The three sets of spindle fibers mentioned above are seen with 

 great clearness. When the spindle fibers are relatively abundant 

 it is readily seen that their arrangement is the same as in repro- 

 ductive cells. 



A marked contrast between the karyokinetic spindle in vege- 

 tative and reproductive cells in the higher plants and especially in 

 the Liliaceae is the small quantity of spindle fibers in the former- 

 This is one of the principal reasons why the process here is more 

 difficult to follow. The spindle fibers are often comparatively few 

 and difficult to stain sufficiently to enable the observer to trace 

 them in detail, and at the same time to prevent over straining of 

 the remaining cytoplasm which would invariably conceal the deli- 

 cate fibers. 



Fig. 14 shows the origin of the cell plate which is laid down 

 here as in pollen-mother cells. The daughter chromosomes which 

 are very regular in this particular case seem to be forming at once 

 a daughter spirem by the union of their free ends. 



