22 AGRICULTURAL AND INDUSTRIAL BACTERIOLOGY 



to be peritrichous. Some investigators recognize another 

 group termed amphitrichous, that is, cells having flagella 

 at both ends. Such organisms, however, are in reality the 

 same as those having flagella at one end only. When a 

 nionotrichous or lophotrichous motile cell is about to divide, 

 flagella frequently develop at the other end so that each 

 daughter cell, following the division of the mother cell, will 

 be motile. The flagella ordinarily point in the direction in 

 which the organism is swimming, that is, they pull the 

 organism about rather than push it. 



Spore Formation. — A spore may be defined as a cell or 

 group of cells set apart specifically for purposes of repro- 

 duction. Usually, though not invariably, spores are more 

 resistant to unfavorable conditions than the cells which 

 produce them. 



Fig. 6. — Spokes of bacteria. 1. Spores centrally located, cells not 

 swollen. 2. Spores central, cells swollen. 3. Spores polar, cells 

 swollen. 4. Spores polar, cells not swolllen. 



Certain kinds of bacteria may produce spores on the 

 inside of the cells. With the exception of two or three 

 little known species a bacterial cell produces only a single 

 spore. Because of their location bacterial spores are some- 

 times termed endospores. It is apparent that inasmuch as 

 a single spore forms within a cell, spore production among 

 bacteria does not involve multiplication or increase in 

 numbers. 



None of the common species of cocci or spirilla produce 

 spores, but some species of the rod-shaped organisms or 

 bacilli do. 



The first evidence of spore formation in the bacterial cell 

 is usually the appearance of certain granules. Gradually 



