62 



BOTANY 



soines arrange themselves in a more or less distinct plate which 

 occupies the equator of the dividing cell. The cytoplasmic fibres are 

 now seen to converge at several points in the cytoplasm, and some of 

 them are connected with the chromosomes, which may each show a 

 sheaf of these attached to it, while other fibres remain free. The 

 several converging points, or poles, in the cytoplasm move toward 

 each other, and usually form two in the long axis of the cell, and 

 at equal distances from the equatorial nuclear plate. The free 

 fibres run from pole to pole, while the bundles connected with the 



FIG. 44. A, pollen mother-cell of Podophyllum peltatum, showing the resting 

 nucleus, with the net-work of nuclear filaments, and the nucleolus. B, late 

 prophase of division ; the nuclear segments (chromosomes) are separate, the 

 spindle-fibres arranged in several groups. (7, completed nuclear spindle; the 

 chromosomes have divided into two. D, part of the nuclear filament of Helleborus 

 fcetidus, showing the chromatin-granules imbedded in the linin-thread. E, a later 

 stage, showing the splitting of the filament. (All figures after MOTTIER.) 



chromosomes are attached to one pole only. The whole mass of 

 fibres is spindle-shaped, hence the whole figure is known as the 

 Nuclear spindle, and the filaments as Spindle-fibres. 



In the nuclear plate the pairs of chromosomes separate, and begin 

 to move toward opposite poles of the nuclear spindle, perhaps due to 

 the contraction of the bundle of spindle-fibres attached to each. It 

 has also been conjectured that the centrosomes, sometimes found at 

 the poles, may be concerned with the attraction of the chromosomes 

 to the poles. Besides the so-called connecting fibres, which run from 

 pole to pole, and the " mantle-fibres," which are attached to the chro- 

 mosomes, there have also been detected, at the outside of the spindle, 



