MITOSIS IN POLLEN MOTHER-CELLS. 



21 



In Fig. 9, C, on the left, is shown a chromosome in metakinesis, 

 which is fastened to the spindle near the middle. Each daughter seg- 

 ment, which is split longitudinally, is in the form of a U-like figure, 



FIG. 9. Heterotypic mitosis. Meta- and anaphases. A, B, C, and F, Lilium. D, Iradescantia. 



E, Podophyllwm. 



A, metakinesis beginning; viewed from the end, each chromosome is seen to consist of four rods, due 



to the second longitudinal splitting, which has taken place at right angles to the first. 



B, metakinesis accomplished; ends of granddaughter chromosomes, which are directed toward equator, 



diverge, giving rise to the well-known V-shaped elements; in B all chromosomes are fastened to 

 spindle fibers at the ends. 



C, chromosome on left was in form of an incomplete ring ; segments fastened at place of bending ; in this 



case the U- or V-shaped elements owe their form to a bending; the chromosome on the right was 

 attached endwise. 



D, mature spindle of Tradescantia. E, F, anaphase; the retreating pairs of granddaughter segments 



are rods hooked at one end, or U's. 



in which one limb seems a little longer than the other. This chromo- 

 some may originally have been a complete ring, as in Fig. 8, E, in 

 which the segments had separated at one end in advance of the other, 



