FORMATION OF SPORES 



55 



of cells representing different generations may appear before 

 the first daughter-cells become free from the original 

 mother-cell. Finally all the cells become full-grown and 

 free, and in turn constitute the mother-cells of future 

 generations. It is mostly by means of this rapid asexual 

 mode of reproduction that yeast is formed in such enor- 

 mous quantities in breweries. 2. The formation of so-called 



FIG. 18. i, Saccharomyc.es cerevisiae ; a, reproduction by 

 budding or gemination ; b, cells containing ascospores. 2, 

 Zygosaccharomyces Barkeri, showing stages in the conjugation 

 of two cells ; in the right-hand fig. four ascospores are present. 

 (Fig. i after Hansen, fig. 2 after Barker.) All highly mag. 



endospores, from two to four in number, within a mother- 

 cell. There is no evidence of any sexual act. Endospores 

 are obtained by placing well-nourished young yeast-cells on 

 moist slices of potato, carrot, etc., well supplied with air. 

 After a few days the protoplasm of the cells undergoes con- 

 centration into two to four masses, each of which becomes 

 surrounded by a cell-wall. When mature, the spores become 

 free by the rupture of the mother-cell. In the Zygosac- 



