THE USEFUL MICROBES 
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split up again into new plants. When a yeast 
cell is placed where there is not enough food 
or moisture, it does not grow by the usual 
method of budding; it breaks up into several 
parts, usually four, called spores, which are 
able to stand drying, heating, or other hard¬ 
ships for a long time. There are many different 
kinds of yeast, and not all of them can form 
spores, though a large number of them do. 
Dried yeast cells are found everywhere in 
nature, being blown about in the air. Yeast 
lives and grows in the soil, in decaying fruit, 
and in many other places. Nearly all kinds 
of yeast require sugar in some form for food, 
and do not grow rapidly where they cannot 
get it. They cannot live on pure sugar, since 
they need certain other things for food also; 
but food-stuffs containing much sugar, such as 
molasses and grape juice, give yeast all it needs 
for its healthy growth. 
One of the big jobs yeast does is called 
fermentation. It is this that makes alcohol 
from sugar. Fermentation breaks up the sugar 
How does 
yeast grow? 
