58 



TISSUES 



formation of the equatorial plate, or else are extruded into the 

 cytoplasm. 



The process which has just been described is termed indirect or 

 mitotic division of the nucleus, also karyokinesis (Schleicher) or mitosis 

 (Flemming). In the opinion of Roux, among others, the complicated 

 nature of mitosis indicates that this process serves to ensure an equal 

 partition of the nuclear substance in general, and of the nuclear reti- 

 culum in particular, between the two daughter-nuclei. The necessity 





U,, 



I 





is 



F 



\ arious stages of nuclear and cell-division, as seen in the growing point of the root 

 of Allium Cepa. Semi-diagrammatic. Explanation in the text. 



for such an equal partition becomes self-evident, if the nucleus, or 

 rather the chromatin, be regarded as the idioplasm or physical basis 

 of inheritance. Hence the longitudinal fission of the chromosomes, 

 by means of which the exact halving of the idioplasm is effected, 

 represents by far the most important stage of the mitotic process. 



The part played by the spindle-fibres during mitosis is not yet 

 clearly understood. Many cytologists regard these " fibres " as elastic 

 threads, which by their active contraction convey the daughter-chromo- 

 somes from the equatorial plate to the poles of the mitotic figure. 

 Strasburger, in fact, discriminates between " traction-fibres " which 



