PLANT DISEASES 



121 



flagella. Bacteria are divided into three easily recognizable 

 divisions: (1) Coccus or spherical bacteria, (2) bacillus or 

 rod-shaped bacteria, (3) spirillum or spiral bacteria. 



Multiplication of Bacteria. — The common method of repro- 

 duction of bacteria is by simple division. Although this 

 method is common to all bacteria, there are some forms 

 which frequently reproduce themselves by the formation of 



Fig. 54. — Several forms of bacteria greatly enlarged. (After A. Fisher.) 



reproductive bodies called spores. The spores are formed in 

 the body of the organism in the shape of small rounded 

 masses, and later the body bursts open and the spores are 

 set free. The spores are known as resting forms and their 

 function seems to be to enable the bacteria to exist through 

 unfavorable conditions. The spores have great vitality and 

 they can be subjected to high temperature and to long periods 

 of drought without suffering from such treatment. 



