22 



A TEXTBOOK OF THEORETICAL BOTANY 



moving away from the equatorial plate in two groups, one of the two 

 chromatids of each original chromosome going into each group. The 

 distribution of chromosomes into the two groups is thus exactly equal, in a 

 qualitative as well as a quantitative sense, and the division is said to be 

 equational. The two groups move convergently towards the two poles 

 of the spindle and form a very characteristic figure, of two radiating clusters, 

 known as a diaster. In this movement the kinetochores lead the way, the 

 arms trailing behind, so that the chromosome looks as if folded in two. As 

 the chromosomes approach the poles the matrix gradually disappears and 

 the double chromonemata again come into view. Their coils relax and they 



^■v>:>-^'- 



CELL PLATE 



StCONDARY 

 SPINDLE FIBRES 



' 5^^'; //,■ ■■■■■; MH^'^' v^^^-'v^^-'-^- '•■•■ 





;#•'**'/; 



B 



Fig. 9. — Vicia faba. Diagram of two successive stages, A and B, in the 

 telophase of mitosis. {After Fraser and Snell.) 



lengthen out, though they retain the relational twist round each other until 

 the prophase of the next mitosis. 



The cause of the movement is still uncertain and has aroused a good deal 

 of controversy, but it is not unlikely that there is, as was first supposed, a real 

 tractive force exercised by the spindle fibres, due to the contraction of the 

 long protein molecules of which thev are composed. 



Mitosis now enters the telophase (Fig. 9), during which the two 

 daughter nuclei are organized. The chromonemata arrange themselves into 

 a reticulum, and in the process they appear to become linked together. If 

 there is any considerable interval between divisions, a finely granular 

 reticulum is formed, in which the individual chromonemata become in- 

 distinguishable, but if divisions follow one another rapidly the reticulum 

 may not be completed and the next prophase follows almost directly. 



Nuclear membranes now appear round the daughter nuclei, and the 

 nucleolus is reformed in each. The relation of the latter body to the chromo- 

 somes is peculiar and interesting. Among the chromosomes in a diploid 



