THE FUNGI 245 
the yeast-cell. It is spherical or ellipsoidal in shape, thin- 
walled, and contains nearly colorless protoplasm, which in- 
cludes oily droplets known as vacuoles and a well-defined 
nucleus. 
Multiplication ordinarily takes place by a process of bud- 
ding by which the nucleus divides and anew cell is pushed 
out from the old 
one and finally cut 
off from it by a new 
cell-wall (Fig. 171). 
Spore formation 
occurs when yeast is 
grown with scanty 
nourishment. The 
protoplasm breaks 
up into small, nearly 
spherical masses, 
often two or four in 
number, and these 
form spores which re- 
sist unfavorable con- a 
st a and 6 show vacuoles; c shows a nucleus 7 inside 
ditions better than © of the yeast-cell; @ shows a budding cell with 
the ordinar east- the nucleus dividing; e shows the cell divided, 
11 yy the new cell containing a bit of the old nucleus. 
cell. 
316. Alcoholic Fermentation. — The growth of yeast in 
a liquid which contains sugar destroys part or all of the 
sugar, changing it mostly into alcohol and carbon dioxide. 
The alcohol remains mixed with the liquid, while most of 
the carbon dioxide escapes in little bubbles. 
In bread making the yeast grows at the expense of sugar 
in the dough (derived from the flour). The bread rises as 
the bubbles of gas escape, at the ordinary temperature, and 
Fie. 171. Common Yeast very Highly 
Magnified. 
