MITOSIS 



FIG. 31. Hyacinth root -tip cell. Chromosomes 

 doubled and with their points of first division 

 in the equatorial plate. 



torial region, but in many cases great indifference is shown in their 



distribution, and it may even be that all ends reach toward the same 



pole, leaving the other side empty 



of chromatin. 



The change from the present 



stage as seen in Figure 30 to Fig- 

 ure 31 is marked by one very 



noticeable fact to which all else is 



subsidiary. This is that every 



chromosome as of one accord 



moves so that the exact middle 



of its length will lie directly in the 



equatorial plane. As an accom- 

 paniment to this, its ends are apt 



to straighten out in a variety of 



directions, so that a definite though 



irregular horseshoe-shaped loop, 



much elongated, is usually the 



result. 



While this is being done, 



another very important change 



takes place. Each chromosome splits for its whole length into two 



halves, the halves remaining at- 

 tached for all their length by an 

 achromatic substance which per- 

 mits of their dual structure being 

 seen. This stage figured in Fig- 

 ure 31 is rare. It is very quickly 

 followed by the stage seen in 

 Figure 32, where it is quite evi- 

 dent that each dual loop is being 

 pulled apart by fibers attached 

 to the apices, one fiber reaching 

 from a pole to one half of each 

 loop, while another fiber from the 

 opposite pole is attached to the 

 apex of each of the other daughter 

 loops. Thus, when these fibers 

 contract, the daughter chromo- 



FIG. 32. Hyacinth root-tip cell. Division of somes are well apart (Fig. 33). 



the chromosomes. ,_. i_ j , / 



They move with ends straight 

 out and form a common and characteristic figure. 



The question naturally arises as to the motive power involved in this. 



