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INTRODUCTION TO BOTANY 



is soon exhausted, and the excretions from the bacteria them- 

 selves interfere with their growth and reproduction. But in 

 situations where bacteria can grow they really do reproduce 

 themselves and increase their number with astonishing rapidity 

 (fig. 166). The possibilities of production and growth of large 



FIG. 166. Gelatin culture of bacteria 



The sterilized gelatin in the dish was exposed in the hallway of a schoolroom for 

 five minutes, and then kept covered for five days, during which time the different 

 colonies of bacteria grew. Each colony grew from one, or possibly, in some cases, 

 from a few individual bacteria, and the number of bacteria that have grown in 

 each colony is so large that the colony is easily seen 



numbers are evident when we remember that many millions 

 of bacteria could live for a considerable time in a cubic inch 

 of milk or beef broth. 



In a few kinds of bacteria the interior of the cell sometimes 

 becomes rounded and inclosed by a relatively heavy wall. 

 This heavy-walled body may remain inactive for a long period, 



