80 



GENERAL BOTANY 



plate. When the wall is complete, the halves of the cell plate 

 form the outer layer of cytoplasm of the newly formed daughter 

 cells, next to the new cell wall. Meanwhile the meshed struc- 

 ture of the cytoplasm appears between each daughter nucleus 

 and the new cellulose wall, which marks the completion of 

 cell division and the formation of the two daughter cells. 

 When one considers that all of the above phases of mitosis 

 are necessary for the formation of each pair of new cells in a 

 growing organism, some conception is gained of the immense 

 constructive activity going on in every growing plant or animal. 



REDUCTION DIVISION AND REPRODUCTION 



The method of cell division, which we have traced above in 

 the cells of root tips, obtains in all vegetative parts of plants, 

 including roots, stems, and leaves, and is hence called vegetative 



FIG. 43. Diagrams designed to show the difference between vegetative and 

 reduction (heterotypical) mitosis 



, ordinary vegetative mitosis in root-tip cells with equal division of chromosomes, 



as in Fig. 43 ; b, mitosis with reduction of chromosomes to one half in each daughter 



nucleus. Further discussion in the text 



cell division (Fig. 43, a). In this type of mitosis the chromosomes 

 which are formed in a cell in prophase (7) line up on the equa- 

 tor in metaphase (2) and split longitudinally to form daughter 

 chromosomes. These daughter chromosomes then migrate to the 

 poles of the spindle (&) and form the daughter nuclei of two 

 new daughter cells (4). By this method of mitosis all cells of 

 the vegetative plant body are supplied with an equal number 

 of chromosomes. 



