MITOSIS 



33 



appeared in each spindle fiber at the equator of the spindle a small 

 thickening. These lie in the same 

 plane and form the cell-plate. 



In Figure 35 one can easily see 

 that the coalescing mass of chromo- 

 somes has become surrounded by 

 a nuclear membrane of somewhat 

 peculiar shape, while the chromatin 

 itself has assumed a spireme-like 

 shape which in proportion and tex- 

 ture much resembles that of Figure 

 27. The whole series of changes 

 through which the chromatin goes 

 in this part of the division process 

 has been compared to a reversal of 

 the earlier changes. It is so to a 

 very limited degree and with re- 

 gard to the chromatin only. Figure 

 35 also shows an increase in the row 



FIG 35. Hyacinth root-tip cell. The nu- 

 cleus divided and the daughter nuclei re- 

 forming. Widening and further cutting off 

 of the cell-plate. 



of dots which have become stronger 



and formed the cell-plate, which is 



the plane through which the two daughter cells are shortly to separate. 



Our last Figure 36 shows the 

 two daughter cells practically sep- 

 arate and complete; the nucleolus 

 has suddenly reappeared ; the chro- 

 matin is nearer to that seen in 

 Figure 26 and can easily be traced 

 to that stage or to the stage shown 

 in Figure 25 or the resting cell. The 

 nuclei are enlarged and rounded 

 in outline and the achromatic fi- 

 brils have all disappeared. It but 

 remains for the two daughter cells 

 to grow in size and then to begin 

 the division cycle over again. 



An Example of Mitosis with 

 Centrosomes. We select the ovum 

 of Unio for the demonstration of 

 mitosis with a complete achromatic 

 figure because of its availability. 

 The ova are found from the early 



days of May to the late days of June in various stages of segmentation. 



FIG. 36. The two daughter cells of hyacinth 

 root-tip. Reappearance of the nucleoli. 



