Io6 MORPHOLOGY AND CULTURE OF MICROORGANISMS 



Forked forms also which are frequently seen are held to indicate longi- 

 tudinal divisions. Some observers have claimed that conjugation 

 occurs among the spirochaetes. If this is true their relation to the 

 Protozoa would be quite likely, but accounts of this phenomenon are 

 inconclusive. Several observers have described "rolled up" specimens, 

 oval and ovoid forms, which have been assumed to be cysts. The 

 spirochaetes break up into granules or short segments and such speci- 

 mens are sometimes spoken of as "monili form." It is not definitely 

 known whether these coccoid forms are simply degenerative forms or 

 the equivalent of bacterial spores. 



Sheaths. — A definite sheath has been described for some forms 

 and the irregularity in the disposition of this around the cell may 

 account for the structures that have been taken for undulating 

 membranes. 



Cell Aggregates. — There is apparently no definite cell grouping but 

 tangled masses of these organisms have been described in several 

 species. 



The Trichobacteria. — ^The trichobacteria are thread or fila- 

 mentous forms. The cells are cyhndrical and similar in form and 

 may or may not vary in size in different parts of the filament. The 

 individual cells are capable of independent existence, but when growing 

 in the filament give evidence of differentiation in function. Some- 

 times these filaments are attached to the substratum or some object in 

 it; at other times they are free. In case of the sessile forms the cells 

 at the attached end (base) are smaller than those at the apex. In 

 other members of the group the ends of the thread are swollen or 

 become club-shaped (Figs. 85 and 86) . In some forms cell division takes 

 place in three directions of space, thus forming a thread of massed 

 cells. 



Branching. — TJ[ie filaments are usually unbranched, but some 

 forms show true branches, such as is found among the plants — fungi 

 and algae. Some again exhibit what is called false branching. This 

 is due to a misplaced cell, which grows parallel or at an angle to the 

 parent thread and suggests branching. 



Reproduction. — ^The cells throughout the filament may divide to 

 form spores, but the apical cells of the thread are frequently set apart 

 for the purpose of reproduction, and by a process of division form 

 spores or conidia. The conidia are usually round and without any 



