194 



General Botany 



Chromosomes and vegetative cell division. In ordinary cell 

 division in a growing tissue a cell near the growing point is more 



Fig. 184. Diagram showing behavior of chromosomes in division of a vegetative eel 

 The daughter cells have the same number and kind of chromosomes as the mother cell. 

 {After Sharp.) 



or less cubical. Cytoplasm and nucleus occupy all the space 

 within the cell wall. The nucleus is very large in proportion to 

 the volume of the cell. Inside the nucleus when properly stained 

 may be seen a tangled network of material called chromatin 

 (Greek : chroma, color) because it may be stained deeply by cer- 

 tain dyes. When the cell is about to divide, the chromatin 

 becomes aggregated into a single much-twisted thread. The 

 thread then shortens and thickens and becomes arranged in a 

 number of loops, and a little later it divides into a definite number 

 of segments, the chromosomes (Greek : chroma, color ; soma,hody). 

 The chromosomes are U-shaped and collect in the equatorial re- 

 gion of the nucleus. By this time lines have appeared in the 

 nucleus radiating from the two opposite poles of the nucleus, 

 forming the so-called spindle. Each chromosome splits longitudi- 

 nally, and a half moves toward each of the two poles. A little 

 later the chromosomes become merged at each pole, granules 

 appear at the equator of the spindle, and the first layer of a 

 transverse wall is laid down. At the former poles of the spindle 

 two new nuclei are organized about the chromatin. The divid- 

 ing wall between the cells is thickened and we have two daughter 

 cells in place of the original or mother cell. This process is re- 

 peated as often as new vegetative cells are formed in roots, stems, 

 leaves, or other organs. 



