344 



THALLOPHYTES 



But a Bacterium commonly forms only one spore, and the 

 formation of spores, therefore, does not generally result in the 

 multiphcation of individuals. The spore stage is apparently for 

 protection rather than for multiphcation. In the spore stage 

 Bacteria can hve where there is no food and when heat and 



Fig. 297. — A petri dish containing agar upon which are colonies of the 

 Bacterium {Actinomyces chromogenus) which attacks Irish Potatoes, causing 

 scabby areas. The white spots are the colonies. From Bulletin 184, Ver- 

 mont Agr. Exp. Sta. 



cold are much too extreme for ordinary life. In this condition 

 some Bacteria can endure boiling water for an hour or longer as 

 well as extremely low temperatures. It is the spores of Bacteria 

 that are hard to kill in sterilizing media and other substances. 

 In the spore stage Bacteria can retain their vitality for months 

 or years and, floating about with the dust in the air, reach all 

 kinds of situations. 



Some Bacteria of Economic Importance 



Bacteria of Decay. — The Bacteria of decay live on dead 

 organisms. By their activity dead organisms, such as straw, 

 weeds, corn stalks, logs, and carcasses of animals, are decomposed 

 into simpler and soluble compounds, in which form they return 

 to the earth and become available nutrients for plants. Their 

 activity helps to rid the earth's surface of debris and to pre- 



