78 



BIOLOGY 



SACCffAROM YCES 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 diam eter. They are so 



showing budding and formation of groups small that almost no internal 



structure can be seen, although 



each one of them possesses a nucleus and a small vacuole 



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 FIQ 32> _ YEAST CELLS MORE HIGHLT 



original cell, and may then MAGNIFIED AND WITH INTERNAL 



break away and become an STRUCTURE SHOWN 



independent cell (Fig. 32), n, the nucleus; 



v, the vacuole; 



Of Several Of them may re- * shows spores in the spore sac or ascus. 



_ 11 u J j. 4-1^.^ t The figures show that in budding the nucleus 



mam attached together tor divide8j K one portioil of it pa8S i ng * in to the bud 



some time, forming a group and the other 



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



