66 Introductory Biology 



II. MITOSIS IN THE CELLS OF FLOWERING PLANTS (Figs. 



22 and 23) 



Mitosis in the cells of the higher or flowering plants resembles the 

 process described for animals, except for minor differences in certain 

 stages (contrast Figs. 20 to 23). 



A. Prophase (Fig. 22, 2-5) 



In the so-called resting stage (nondividing), the nucleus is separated 

 from the surrounding cytoplasm by the nuclear membrane; the deeply 

 stained nuclear granules are in the form of chromatic strands. When a 







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Fig. 22. — Mitosis in plants. 1, Before mitosis begins, strands of chromatin ap- 

 pear as a granular network within the nucleus. Prophase stages: 2-5, Network 

 tends to disappear and the chromatic strands thicken and shorten, eventually 

 forming a specific number of chromosomes; each chromosome consists of two 

 darkly stained chromatids more or less in contact with one another and which 

 will separate when each chromosome divides lengthwise later; in stage 5 the 

 spindle is forming and the nucleolus disappearing. Metaphase stage: 6, Chromo- 

 somes line up on equatorial plate in the middle of the spindle which has just 

 been completed. Anaphase stages: 7 , Each chromosome divides lengthwise into 

 two equal parts. Each new or daughter chromosome moves along the spindle 

 toward opposite ends of the cell. 8, Chromosomes at ends of the cell; cell wall 

 begins to form as minute swellings appear on each spindle fiber at the equatorial 

 plate. Telophase stages: 9, Chromosomes disintegrate again into a network of 

 chromatin granules; nuclear membrane appears; cell wall continues to develop; 

 spindle disappears. 10, Mitosis complete; cells similar to the original cell but 

 smaller; nuclei and cell wall complete. The two daughter cells will now grow 

 to normal size. (Copyright by General Biological Supply House, Inc., Chicago.) 



