PURPOSE OF MULTIPLICATION OF CELLS 



277 



the original capacity of division and thus constitute generative 

 layers, cambium, or phellogen, or growing regions. 



The increase in amount of living material of the cells formed 

 by the generative layers, and the consequent increase in volume 

 of these cells, accompanied by more or less morphological differ- 





Fig. 131. Changes in nucleus during mitotic division. A, earliest observable 

 stage, showing a coarsely granular thread of filament. B, a later stage in which the 

 thread is arranged in parallel segments (chromosomes), and the cytoplasm (not 

 shown) begins to arrange itself around two poles. C, D, arrangement of the seg- 

 ments or chromosomes in the nuclear plate, and showing the spindle fibers. £>, E, F, 

 showing longitudinal division of the chromosomes. G, H, separation of the newly 

 formed chromosomes, and movement toward the poles of the nuclear spindle. J—P, 

 stages in which the daughter chromosomes collect and fuse into the nuclear substance 

 of the daughter nuclei. M, N, the spindle fibers connecting the daughter nuclei 

 remain, and midway between the nuclei may be seen an aggregation of finely granu- 

 lar material, which finally fuses together in a continuous membrane, the cell-plate, in 

 O, and forms a wall in P. After Strasburger. 



