GROWTH 



207 



nucleus, which by this time has assumed the configura- 

 tion of a spindle, with a striped appearance (these stripes 

 are not stained, hence the substance which forms them is 

 called achromatin, fig. 59, C) . When the chromatin has 

 gathered at the poles and become bunched up together, 

 so that we have already two nuclei (fig. 59, D) and 

 division of the nucleus is complete, the division of the 

 cell begins. Again in the equatorial plane of the 



Ai'y.- 



-^L 



Fig. 59. 



spindle, there appear minute grains (fig. 60, i) which 

 blend later on into a kind of plate consisting of the 

 same substance as the cell-wall, i.e. of cellulose (fig. 60, 2) . 

 As it forms, this plate pushes itself against the cell-wall, 

 and we see a partition dividing the cell into two parts 

 (fig. 60, 3). Each of the newly-formed cells has a 

 nucleus of its own, and starts an independent existence, 

 grows, and on reaching a certain dimension divides 

 in its turn. 



We had before a general explanation as to why the 

 plants elongate more quickly in the dark. This depends 



