CHAPTER X 



CELL DIVISION 



We have already learned that the growth of the plant involves 

 an increase in number and size of the cells. In many of the 

 lower plants this division is by a very simple process, but in the 

 higher plants it is the result of a very complicated process known 

 as mitosis. 



The term " mitosis " is used to designate the complicated 

 internal processes of cell division. We have already studied the 

 structure of the cell (Chapter I). The protoplasm is the living 

 part of the organism and can be divided into the cytoplasm or 

 constructing part, the plastids (Chapter I) and the nucleus or 

 controlling part. 



The nucleus is composed of the chromatin, which is a 

 tangled thread of colorless substance that absorbs artificial 

 stains very readily, and is considered its most important part; 

 the nucleoli, and the limin, which is a network of very deli- 

 cate threads. 



The first evidence of cell division (Fig. 90) is the enlarge- 

 ment of tie nucleus which contains the linin (or the network of 

 delicate threads) the nucleoli and chromatin. The chromatin is 

 very definitely associated with the linin. It increases in 

 amount, becomes ribbon-like in character and finally divides into 

 short pieces called chromosomes. Their number is constant for 

 each species, but varies in the different species of plants. At 

 about this time the nuclear walls disappear and delicate color- 

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