BACTERIA 107 



resting stage may produce new threads of cells. Sometimes spores 

 germinate while still in the old thread (Fig. 85), giving a tangled 

 mass of cells or whorls of new threads at intervals on the old. The 

 conidia may be either motile or non-motile. The motility of these 

 conidia when it exists is due to flagella. 



Shaath. — ^The threads of cells are sometimes surrounded by sheaths 

 of varying thickness. This sheath is a thickened and hardened mem- 



FiG. 85. — Crenothrix polyspora Cohn,'Brunnenfaden. (,After Migula from Schmidt 



and Weiss.) 



brane, and forms a tube in which the different cells of the bacteria are 

 contained. This sheath is homologous to a capsule. In it are fre- 

 quently deposited characteristic by-products of the cell. In Creno- 

 thrix (an iron bacterium), for example, we have iron oxides. 



The best-known member of this group is the water-pest bacterium 



