144 THE CYTOLOGY AND LIFE-HISTORY OF BACTERIA 



Cell-division is transverse, as in all other bacteria, although the stalk is 

 attached to one end of the cell. One daughter cell therefore remains attached, 

 the other develops a flagellum and swims away until it encounters a suitable 

 substrate, upon which it settles. A stalk is developed and the flagellum de- 

 generates. This process is really a simple life-cycle with alternate sessile and 

 free-living generations (Chapter VII). 



J: SUMMARY 



Bacteria may form multicellular structures of several different types. 

 In some of these there is a certain degree of specialisation of function between 

 the constituent bacteria, in others little or none. In the myxobactcrial fruiting 

 body the majority of bacteria are transformed into reproductive microcysts, 

 the minority become " somatic " cells in the stem or wall, and are sacrificed. 

 This is also true, in a greater degree, of streptomyccs. The main body of the 

 colony is sessile and vegetative, the spores alone are reproductive, and are 

 borne upon a special, reproductive mycelimn. A similar specialisation of 

 function divides the sessile and motile cells of chlamydobactcria and caulo- 

 bactcria, and the swarming and non-swarming units of Proteus. 



Streptomyccs colonies are single units, arising from a single spore. In 

 eubacteria and myxobacteria the unit is the swarm or vegetative culture. 

 The myxobactcrial fruiting body is a device which ensures the distribution 

 and survival of swarms, as such. In the eubacteria distribution may be of 

 single cells or of portions of swarms, usually the latter. Eubacterial colonies 

 have no intrinsic form, unlike fruiting bodies, their structure is due to the 

 interaction of the forces of growth of the cells and mechanical resistance of 

 the environment. The swarm has little co-ordination except in myxobacteria 

 and Proteus. 



BIBLIOGRAPHY 



(i) BissET, K. A. (1938) J. Path. Bact. 47. 223. 



(2) BissET, K. A. (1939a) ibid. 48. 427. 



(3) BissET, K. A. (1939b) ibid. 49. 491. 



(4) Erikson, 13. (1947) J. Gen. Microbiol, i. 45. 



(5) Fischer, A. (1897) Vorlesungen uber Bakrcricn. Leipzig. 



