KARYOKINESIS ID3 



spherical body bounded by the nuclear membrane and 

 containing a network or detached granules of chromatin 

 bathed by a liquid, the nuclear sap. The nuclear mem- 

 brane and chromatin are doubtless of gel structure, the 

 nuclear sap a sol. There is also present in most cases 

 a conspicuous spherical deeply staining body (sometimes 

 more than one) called the nucleolus. This seems to 

 be of the nature of reserve material which is used to 

 " feed " the chromatin when division occurs. The 

 nucleus in this condition is often called the " resting 

 nucleus," because it is not dividing, butjthe term is 

 rather misleading, for the nucleus is really carrying out 

 its main function, that of " directing " the nutrition 

 and growth of the cell. 



Division of the Nucleus (Karyokinesis) and of the 

 Cell. — Meristematic cells constantly divide, and between 

 two successive divisions there is a period of growth 

 (increase in bulk) of the protoplasm till each daughter 

 cell attains about the size of the mother cell before 

 division, when each divides again. The division of 

 the cell is always preceded by division of the nucleus, 

 which takes place in a remarkable, complicated fashion, 

 the process being known as karyokinesis ' or mitosis » 

 (Fig; 7, G). Except in the nuclear divisions preceding 

 the formation of the reproductive cells, this process 

 of karyokinesis shows substantially the same features 

 in every nuclear division preceding cell division in 

 practically all animals and plants, the differences met 

 with being of quite minor importance. 



The chromatin granules (or chromatin network 

 [Fig. 8, a\) of the " resting nucleus " become arranged in 



1 Greek Kotpvov, a nut (nucleus), Klvrjau;, motion. 



2 From Greek fiirdca, to stretch the warp in the loom, because of 

 the thread structures appearing in the process. 



