Structure, Growth and Distribution. 5 



to form packets of cells resembling a bale of binder 

 twine (sarcina), while many forms show no regularity 

 in the grouping of the cells. But few of the bacilli and 

 spirilla show a characteristic grouping of the cells. 



Spores of bacteria. The seeds of plants are not so 

 easily injured by heat, cold, or drying as are the grow- 

 ing plants which bear them. The seeds thus carry over 

 the plant from one growing season to the next. Many 

 kinds of bacteria form within the cell a tiny structure, 

 called a spore, which is much more resistant than the 

 vegetating cell, and hence, in this respect is comparable 



FIG. 4. SPOKE FORMATION AND GERMINATION. 

 Figures on upper line show various stages of spore 

 development. Lower left hand figure represents 

 the cell issuing from the spore case. 



to the seeds of ordinary plants. The spores are, how- 

 ever, much more resistant than the seeds of any of the 

 higher plants. Boiling for hours will not kill some 

 kinds of bacterial spores. They can be dried for years 

 and still grow quickly when placed in a favorable food- 

 material. Thus, the bacteria forming spores are able 

 to withstand unfavorable environmental conditions. 



The spores are unlike seeds in that spore formation 

 is not to be considered as a manner of increasing in 



