44 COMPENDIUM OF GENERAL BOTANY. 



(c) Division of the plasm with partial membrane-formation 

 which occurs subsequently. 



(d) Cell-formation by budding. 



In (a) the mother-cell divides into two, more rarely many, 

 daughter-cells. As in type III they receive a complete new mem- 

 brane, but differ in that the entire contents of the mother-cell are util- 

 ized. Example : spore-formation among certain moulds (Fig. 119). 



(J) This is the more usual form of cell-division in tissue-forma- 

 tion. Internal causes bring about a division of the plasm ; then sud- 

 denly the cellulose-membrane makes its appearance, usually at right 

 angles to the wall of the mother-cell. Hence the daughter-cells possess 

 in part the membrane of the mother-cell. In sharp contradistinction 

 to (c) no intermediate form with incomplete septa can be observed. 



(c) The primordial utricle becomes constricted. (In cylindrical 

 cells, for example, there appears a circular fold.) Finally, when this 

 constriction has progressed to the middle point, the two portions sep- 

 arate. Immediately following this process the cellulose- wall begins 

 to form from without inward, sometimes presenting the appear- 

 ance of a constricting membranous fold actively encroaching upon 

 the primordial utricle. But the cell-membrane can only grow by 

 means of the nourishing plasm ; the plasmic constriction is therefore 

 primary. Example: the algal genus Spirogyra. Since such divi- 

 sion usually occurs in darkness, it is advisable to place the algae in 

 the dark before examining them ; or the algae may be selected at 

 iiight and placed in alcohol to be examined the following day. By 

 proper management all intermediate stages of cell-wall formation 

 may be found. 



(d) Budding. The mother-cell develops a bud which becomes 

 independent by the formation of a septum. The bud may finally 



become entirely separated. Example : Sacharo- 

 myces cerevisice* the fungus of beer fermentation 

 (Fig. 25). 



Among these plants (Sacharomyces) the inter- 

 esting discovery has been made (REES) that they 

 FIG. 25. reproduce differently under different external sur- 

 roundings. In the usual medium (beer) budding is the prevailing 

 mode of reproduction. If simply kept moist, for example, upon 

 slices of potato, the fungus reproduces by free cell-formation 

 (ascospores). Cell-formation by budding is also typical among 

 the Basidiomycetes. 



