1898] KARYOKINESIS IN THE ROOT TIPS OF ALLIUM CEPA 231 
times the figures of the metakinesis stage are remarkable for 
their symmetrical development (figs. 29, 30). Such symmetry 
could not be present were the two ends of the spindle formed 
at haphazard from variable numbers of irregular smaller ele- 
ments. The centrosomes usually divide during metakinesis 
(figs. 31, 32). By the time the daughter chromosomes have 
arranged themselves around the poles, the centrospheres, as a 
general rule, have divided and the radiations show more promi- 
nently than in the earlier stages (fig. 23). The chromosomes 
now begin to contract and the free ends turn inwards, while at 
the same time the threads of the central spindle become thick- 
ened and stain much deeper than before. The polar radiations 
also become more widely separated because of the outward pres- 
sure exerted by the chromosomes (fig. 34). At the time when 
the chromosomes are curving inward the central spindle threads 
begin to bulge outwards, and the cell plate is formed from the 
center, appearing at first as granular thickenings in the spindle 
threads. In this stage the centrospheres often appear still 
united but containing a double centrosome (figs. 35,36). In 
Jig. 37 only one centrosphere is visible at the upper pole, the 
other one lying immediately beneath the one in view. 
The central spindle continues to bulge outward and the cell 
plate becomes larger, until finally when it reaches the cell walls 
the spindle has a very,flattened appearance (jigs. 38,39). The 
spindle threads continue to stain very dark at the center until 
the cell plate is complete. What the cause of this dark stain- 
ing may be was not discovered. It was probably due to the 
presence of various materials in the thickened spindle threads 
which are used in the formation of the cell wall. It is not easy 
to understand how the threads of the central spindle extend 
outward until they are sometimes almost doubled on themselves. 
But whatever the direct cause, they are considerably longer 
than they were at first. The central spindle threads disappear 
as soon as the cell wall is well formed, being absent in the 
center while they are still prominent in the outer regions (fig. 
39). As soon as the cell wall is complete the threads disappear 
