﻿262 BOTANICAL GAZETTE [april 



merits in such a manner that the resulting pairs of segments are 

 identical with the pairs of granddaughter segments of the first 

 division. In those cases to be mentioned in a later paragraph, 

 in which the daughter nucleus closely approaches or passes into 

 the resting^ stasfe, it is readily seen how much more difficult the 



fc» """O 



problem is. 



A glance at those stages of the process represented \xi figs. 

 12, 1 J, 14, and /J will give some idea of how the long and entan- 

 gled chromatin segments are gradually brought to a more regular 

 arrangement in the nilclear plate, although in species of Lilium 

 with long chromosomes the arrangement, as a rule, is not very 

 regular. The twisted and contorted form of the chromosomes 

 seems to be due chiefly to the irregularity of the spirem. 



During the transformation of the multipolar into the bipolar 

 spindle, the entangled collection of chromosomes seems to be 

 gradually pulled, pushed, and untangled into the more regular 

 arrangement of the equatorial region, and there can be little doubt 

 that the spindle fibers are primarily active in bringing each pair 

 of chromosomes into its proper place. 



As already stated, the segments of the chromosomes in the 

 nuclear plate lie generally side by side and more or less twisted 

 about each other. Sometimes the free ends of the sesfments 



diverge widely, those which are fastened to the spindle fibers 

 being in contact or even separated a little. This phenomenon 

 has been interpreted by some observers as metakinesis, but such 

 a condition is sometimes met with before the spindle is mature. 

 The spindle fibers have an orientation similar to that of the first 



-A 



mitosis. 



As the segments separate during metakinesis, the nuclear 

 plate presents a complicated picture {^fig^ 16). This phenome- 

 non is due to the twisted condition of the chromosomes previously 

 mentioned. On their way to the poles the segments may 

 straighten out somewhat. Each is then usually a long and fre- 

 quently undulating or bent rod, that is generally hooked at the 

 end to which the spindle fibers are attached {figs, 17 ^ ^^)- 

 Sometimes the chromosomes are attached near the middle, in 

 which case the retreating segments will be in the form of a V 

 or a U. 



