SECT. I 



89 



mences as a ring-like projection from the inside of the wall of the 

 mother cell, and gradually pushing farther into the cell, finally extends 



FIG. 93. Cell of Spirogyra in division. FIG. 94. Portion of a dividing cell of Clado- 



n, One of the daughter nuclei ; w, de- phora fracta. w, Newly-forming partition 



veloping partition wall ; ch, chloroplast wall ; eh, dividing chromatophore ; k, 



pushed inward by the newly-forming nuclei, (x 600.) 

 wall. (X 230.) 



completely across it (Figs. 93, 94). In a division of this sort, in 

 uninuclear cells, nuclear division precedes cell division, and the new 

 wall is formed midway be- 

 tween the daughter nuclei 

 (Fig. 93). In the multinuclear 

 cells of the Thallophytes, on 

 the other hand, although the 

 nuclear division does not differ 

 from that of uninuclear cells, 

 cell division (Fig. 94) is al- 

 together independent of nuc- 

 lear division. And in multi- 

 nuclear, unicellular Thallo- 

 phytes, nuclear division is not 

 followed by a cell division. 



The interdependence of 

 nuclear and cell division in 

 uninuclear cells is necessary 

 to ensure a nucleus to each > 



daughter cell. In multi- -SffillS 

 nuclear cells it is not essen- 

 tial that cell division should 

 always be accompanied by 



nuclear division, as in any FIG. 95. Portion of the peripheral protoplasm of the 



Case a Sufficient number of embryo-sac of Keseda odorata, showing the commence- 



T . .,, , , ,. ment of multicellular formation. The process pro- 



nuclei will be left to each gresses from above downwards . (x 240 .) 

 daughter cell. 



Free Nuclear Division and Multicellular Formation. The nuclear division in 



