238 



THE CELL 



divided into two cells. Fig. 390. In some cases, however, 

 the nucleus divides many times without the formation of a 

 cell -wall. The cell which began to divide is called the 

 mother cell, and the resulting cells are daughter cells. 



392. Cell bud- 

 ding is a variety of 

 cell division in which 

 the cell is not di- 

 vided in the mid- 

 dle. The mother 

 cell pushes out a 



390. Four steps in process of cell-division. 

 Mother cell at left, far advanced in division; daughter protuberance, which 



cells at right. becomes separated by 



a constriction of the walls. Cells of the yeast plant and 

 the spores of many fungi multiply in this way. 



393. In no case, so far as we yet know, can the cell 

 divide without a division of the nucleus and the protoplas- 

 mic mass. There are two methods of nuclear division: (1) 

 direct, as found in the old cells of nitella, tradescantia, and 

 others, in which the mass of the nucleus divides by simple 

 constriction; (2) indirect, as found in all actively growing 

 tissue, in pollen grains, spores, etc. There are several 

 stages in the latter process. The nucleus divides in intri- 

 cate methods, giving rise to odd forms known as nuclear 

 figures. Mitosis and karyokinesis are names sometimes 

 given to indirect nuclear division. The study of this pro- 

 cess is a very difficult one, as it requires a very high power 

 microscope to see the different stages. They are easily 

 seen in cells found in buds of convallaria and in pollen 

 grains of that plant, but may be studied in all plants. The 

 process is too difficult for the beginner to trace, but it is 

 outlined in the note on next page. Fig. 390 is not intended 

 to represent all the stages in indirect nuclear division. 



Eeview. What are some of the forms of cells? Name the parts 

 of a living cell. What part or parts are essential in all cases? Give 



