24 AGRICULTURAL BACTERIOLOGY 



of life, one finds transition forms that have the char act er- 

 istics of both of the related groups to a greater or less 

 degree. Such forms occur between the true bacteria and 

 the true molds, or, more properly speaking, the filamentous 

 fungi. The term higher bacteria, or trichobacteria, is ap- 

 plied to these in opposition to the haplobacteria, or strictly 

 unicellular forms. 



The higher bacteria occur in threads or filaments. A 

 number of cells are contained in a common sheath. It is 

 probable that the individual cells are capable of indepen- 

 dent existence. Since they occur in filaments, they give 

 evidence of a certain differentiation in function. Some of 

 the cells are concerned with reproduction, others with the 

 anchoring of the -thread to its substratum. In such organ- 

 isms is found the beginning of the division of labor, the dis- 

 tinguishing characteristic of the higher forms of life. The 

 filaments are usually unbranched. Some, however-, show 

 true branching, a property that allies them to the molds. 

 Still others have false branching, due to the misplacement 

 of a cell in the thread. A cell forced out of its position in 

 the chain by its division gives rise to a new thread. 



Another property that allies the higher bacteria to the 

 molds is the production of spores, or conidia, by the divi- 

 sion in the three dimensions of space of the upper cells of 

 he sessile thread. The conidia are motile in some instances ; 

 in others, non-motile. They leave the sheath in which they 

 have been formed, and float away to establish new threads 

 vhen they lodge on a favorable substratum. The spores may 

 germinate while still in the sheath, giving rise to a whorl 

 of threads. 



Among the higher bacteria are to be found some of great 

 practical importance, such as the iron bacteria, which fre- 

 quently cause the clogging of water-mains and drains ; and 



