NATURE OF PLANTS 



57 



division delicate colorless strands begin to appear and ultimately 

 grow into a spindle as shown in Fig. 31, D. There are two sets of 

 these strands or fibrillae; an inner and an outer series. The outer 

 fibrillae, in some way not understood, arrange the chromosomes in 

 the center or equator of the spindle (Fig. 31, D) where each 



A D 



FIG. 31. Cell division in root of corn: A, cell with nucleus enlarging pre- 

 liminary to division /, linin; ch, chromatin. The central dark body is the 

 nucleolus. B, later stage, the chromatin has increased and appears as a ribbon- 

 like skein. C, formation of the chromosomes, cr. D, formation of the spindle 

 and the arrangement of the chromosomes in the center of the spindle. 

 I. D. Cardiff. 



chromosome divides by a longitudinal division into two equal 

 parts. The fibrillae now separate the two halves of each chromo- 

 some and pull them to the opposite poles of the spindle so that 

 each pole receives a half of every chromosome (Fig. 32, E). 

 The chromosomes now become rearranged at the poles and two 

 new nuclei are gradually formed like the original nucleus (Fig. 

 32, F, G). In the meantime the inner fibrillae of the spindle have 

 shortened and become thicker at the equator (Fig. 32, G). This 

 thickening goes on assisted by the addition of new fibrillae at 

 either side of the spindle until a delicate line (the cell wall) reaches 

 across the old cell (Fig. 32, H), and the division of the mother 

 cell into two daughter cells is completed. In this way new cells 

 are being constantly added to the root. It will be noticed, if a 

 longitudinal section through the middle of the root is examined, 

 that various regions of the elongating root may be recognized 

 owing to the difference in the character of their growth. In such 

 a section (Fig. 33) we see that the tip of the root is covered with 

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