BOTANY 



be termed traction-fibres, those which run from pole to pole supporting- 

 fibres. The nucleoli appear to form a reserve substance which serves 

 to nourish the chromosomes and, later, has the special duty of provid- 

 ing material for the formation of the spindle. Any excess of nucleolar 

 substance passes into the surrounding cytoplasm, where it forms the 



FIG. 86. Successive stages of nuclear- and cell-division in a meristematic cell. ., Nucleus; nl, 

 nucleolus ; tc, nuclear membrane; e, cytoplasm; eh, chromosomes; k, polar cap-.; s, spindle; 

 kj>, nuclear plate ; t, young daughter nuclei ; c, connecting fibres : z, cell-plate ; m, new cell 

 wall. In 1, the resting nucleus ; 2 and 3, separation of the chromosomes ; 4, chromosomes with 

 transverse discs ; 5, the arrangement of the chromosomes to form the cell plate and their 

 longitudinal fission ; 3-5 show the formation of the spindle from the polar caps ; r., the longi- 

 tudinal fission of the chromosomes ; 7, the beginning of their separation to either pole ; 8, the 

 complete separation of the daughter chromosomes; 9, jwssage of the daughter chromosomes 

 to either pole ; 10-12, formation of the daughter nuclei ; in 9-11 the origin of the connecting 

 fibres and of the cell plate is seen, while in 12 the new cell-wall is formed. ( x alnnit 000.) 



so-called extranuclear nucleoli. The traction -fibres promote the 

 arrangement of the chromosomes in the equatorial plane (5). After 

 the chromosomes have split longitudinally into the daughter chromo- 

 somes, the latter are separated and drawn towards the two poles by 

 the contraction of the traction-fibres (8, 9). The supporting-fibres 

 afford the necessary resistance in the process. The spindle fibres can 

 often be traced to the limiting layer of the cytoplasm, and their 



