78 



BIOLOGY 



n 



SACCHAROMYCES YEAST 



The yeast is a plant slightly smaller than Pleurococcus but 

 resembling it in its general shape, although it differs in some 



important respects. It is made 

 up of single cells, usually slightly 

 oval in shape, although some- 

 times they are elongated and 

 occasionally spherical; see Fig. 

 31. These organisms are ex- 

 tremely minute in size, not 

 being more than 1/4000 of an 

 FIG. 31.- YEAST CELLS inch in diameter. They are so 



Showing budding and formation of groups Small that ahllOSt no internal 



structure can be seen, although 



each one of them possesses a nucleus and a small vaouole 

 which is not contractile; 

 Fig. 32. As each of these 

 bodies possesses a nucleus, 

 it is a cell, and thus we see 

 that the yeast is made up 

 of clusters of single cells. 



Reproduction. The 

 method of reproduction of 

 yeast is by the growth of 

 buds on the side of the old 

 cell. The bud appears first 

 as a swelling, which grows 



until it is the size of the FlQ 32 YEAST 



original cell, and may then 

 break away and become an 

 independent cell (Fig. 32), 

 or several of them may re- 

 main attached together for 



SOme time, forming a grOUp and the '^remaining in 'the mother c< 



of more or less independent cells. This process is called budding. 



CELLS MORE HIGHLY 

 MAGNIFIED AND WITH INTERNAL 

 STRUCTURE SHOWN 



n, the nucleus; 

 v, the vacuole; 



s, shows spores in the spore sac or ascus. 

 The figures show that in budding the nucleus 

 one portion of it passing into the bud 



