THE PLANT-CELL 



63 



free fibres which are attached at one end at the poles, but end free 

 in the surrounding cytoplasm. 



Anaphases. As the chromosomes approach the poles of the spin- 

 dle, they become crowded together, and finally grow together, end to 

 end, and constitute a single filament, which gradually assumes the 

 condition found in the resting nucleus. The nucleolus is formed 

 again, as well as the nuclear membrane, and the nucleus has now all 

 the characters of the typical resting nucleus. 



Cell-plate. While the two groups of chromosomes are moving 

 toward the poles, there suddenly becomes evident, in the equator of 

 the spindle, a disk, formed of small granular bodies, which finally 

 coalesce into a continuous membrane, the Cell-plate. The granules 

 of which the young cell-plate is composed are formed by swellings 

 in the connecting fibres, whose substance, apparently, is transformed 

 into the elements of the cell-plate. In case the Cell-plate does not 

 extend entirely across the cell, new elements are added to its margin 

 by the peripheral spindle-fibres. The cell-plate finally splits into 

 two lamellae, and thus the division of the protoplast is completed. 

 The new cell-wall is then deposited in the space between the proto- 

 plasts, in the same way that 

 a cell-wall is formed upon the 

 surface of a naked protoplast, 

 such as a zoospore. 



The changes in the nucleus 

 up to the formation of the 

 nuclear plate are known as 

 the Prophases ; the separation 

 of the chromosomes and their 

 movements to the poles, the 

 Metaphases; the reconstitu- E 

 tion of the daughter-nuclei, 

 the Anaphases. 



Direct Nuclear Division. 

 Sometimes in large cells, like FIG. 45. Direct (amitotic) nuclear division 

 the internodes of the Characete, in an intemodai cell of Chara fra^ilis 



, , e (X 750) ; n, dividing nuclei, 



and those in the stem of 



Tradescantia, the nucleus may become constricted, or divided directly. 

 This is known as direct or amitotic division, but only occurs in old 

 cells, and is never accompanied by a division of the protoplast 

 (Fig. 45). 



Budding 



The form of fission known as budding consists simply in a protru- 

 sion of the cell-wall, which is then separated from the parent-cell by 

 fission. This occurs regularly in the Yeast-fungi, and is also seen in 

 the branching of many filamentous Algae. 



