CELL-DIVISION. 



113 



chromosomes close to the poles of the spindle ; this stage is also 

 known by the terms — donble-rosette or diaster-stage (see Fig. 

 79, 8, Fig. 80, 9, and Fig. 88). On the lines of the chemotactic 

 theory, the passage of the two systems of chromosomes is efifected, 

 not by the agency of the mantle-fibres of the achromatic spindle, 

 but by the attractive influence of certain substances in the 

 vicinity of the poles of the spindle (enzymes) upon the chromo- 

 somes ; nevertheless, distinct cone-shaped bundles of the spindle 



Fig. 88.— A Mbtaphasb St4.ge from Allium Root-tip, showing two 

 systems orioops widely separated (from a photomicrograph). 



fibres can be seen attached in many cases to separate chromo- 

 somes along their whole length, so that the theory of the pulling 

 action of the mantle-fibres cannot be lightly dismissed. It is 

 possible that a compromise must be made, both chemotaxis and 

 the action of the mantle-fibres being taken into account. 



(y) and (8) The ^Aaiapha^e and Telophase ; formation of the 

 : cell-plate. — The final or end-stages in mitosis comprise (a) In- 

 volution of the secondary chromosomes, and (6) The formation 

 of the cell-plate. 



