VEGETABLE HISTOLOGY AND PHYSIOLOGY. 149 



379. #, Conjugation. New cells are also produced 

 by the union of the protoplasm of two or more cells; 

 the contents of which having commingled, the com- 

 bined mass incloses itself with a cellulose covering, 

 and becomes a new cell. 



380. 3, Fission is the name applied to the mode of 

 cell production by which two or more new cells are 

 formed out of one. This is the usual mode, and may 

 be treated under three heads. 



381. a. Fission Proper. A young complete cell (Figs. 

 465, 466) possesses the power to multiply. The most 

 simple case of this process is the division of the cell 

 into two equal, or nearly equal, parts. The protoplasm 

 forms two nucleus-like spots ; a stricture then com- 

 mences in the wall between the spots, and the cell 

 seems to pinch itself into two. This process is shown 

 in the fission of Bacterium cells (Figs. 511, 512). 



In most cases the process is accompanied by a 

 stricture more or less prominent ; at the same time 

 an equatorial septum appears between the nuclear 

 spots, and divides the old cell into two nearly equal 

 new cells (Fig. 476). In this case the stricture in the 

 cell-wall is barely visible. The new cells round up and 

 soon become sub-globular in form. 



476, Phases of a cell undergoing the process of fission ; a, complete cell with drops of cell-sap among 

 the protoplasm, nucleus, and nucleolus ; 6, same, with nucleus and nucleolus divided ; c, with stricture 

 and wall forming across between the nuclei; <Z, same, with the septum completed, and the fission accom- 

 plished; two separate cells have been formed by dividing the old cell into two. 





