CELL-DIVISION. 101 



In some cases of free cell-formation the nuclei may divide 

 amitotically. the cytoplasm of the original cell becoming distri- 

 buted round the several nuclei resulting from the division. 

 Cell-walls may be subsequently formed cutting off separate cells 

 from one another. The formation of endosperm in Phanerogams 

 takes place in a somewhat similar manner, although mitosis is 

 here the usual type of division of the nuclei.* 



B. Mitotic Nuclear Division, followed by division of the cell. 



1. This process almost always precedes division of the cell in 

 Higher Plants and most of the lower plants, although in the 

 latter case differences may be seen during some of the phases. 



In order to properly understand mitosis, it is necessary first of 

 all to examine more fully than has been done hitherto the 

 structure of the quiescent nucleus. To do this, powers of the 

 microscope, ranging from the -J inch to the y\- inch oil immersion, 

 should be employed, and preparations of the cell for the purpose 

 of examining the nucleus should preferably be made in the 

 manner described in the Note at the end of Chapter ii., young 

 growing tissues, such as a root-tip of Allium or Hyacinthus 

 serving very well for material to work with. The preparation 

 having been made, a cell should be selected for examination in 

 which the nucleus is still intact, and as yet shows no signs 

 of karyokinesis. Such a nucleus will, under the yV inch objective 

 and a suitable eyepiece of the microscope, be magnified about 

 •800 or 900 diameters, and will show the following structure 

 (see Fig. 76, 1, Fig. 81a, and Fig. 1) :— 



[a) All external boundary, the nueleaP membrane, which is pro- 

 bably the innermost firmer portion of the kinoplasm, or layer of the 

 cytopla-sm just outside the nucleus. The nucleus may, in fact, be looked 

 upon as a space filled with fluid and bounded by the kinoplasm, in which 

 space certain other structures are suspended 



(6) Internal to the nuclear membrane, a clear portion, of a fluid nature, 

 the so-called nuclear plasm, in which are suspended : 



(c) A network of a material known as linin. This is not easy to 

 detect, except by very careful focussing. 



(d) Granules of a substance known as Chromatin, arranged at some- 

 what irregular intervals upon the linin network ; here and there rather 



* Such a formation of cells is sometimes known as "multicellular 

 formation." Free cell-formation results in the production of distinct 

 isolated cells, as in the case of the production of ascospores in the Fungi. 



