LIFE-CYCLES IN BACTERIA 121 



What is known of the cycle in Mycohacterintn and Nocardia is entirely com- 

 parable in most respects (Chapters V and VI), but these organisms have some 

 characters in common with the higher bacteria, to which they are probably 

 related. 



D; THE LIFE-CYCLE IN HIGHER BACTERIA 



(32, 37) 



hi streptomyces a truly multicellular organism is formed, and thus the 

 problem of distribution entails the hberation of free, reproductive units, small 

 airborne spores. Streptomyces resemble moulds in their general form, and 

 this resemblance extends to their mode of reproduction. 



The spore alights upon a suitable substrate, and germinates to form the 

 primary mycehum. Sexual branches arise upon the primary mycelium and 

 initiate the aerial hyphae which bear the spores. 



During its hfetime the organism or colony produces spores continuously, 

 while conditions are suitable, hi eubacteria, upon the other hand, the re- 

 productive cells arise only in an ageing culture, when almost all may be thus 

 transformed. 



The true Actinomyces hovis, which is a parasite and microaerophilic also 

 has a complete life-cycle with a primary and secondary mycelium. But the 

 spores, which cannot be expected to benefit by aerial distribution, are borne 

 singly and in relatively small numbers. This may represent a degenerate 

 condition. 



E: THE LIFE-CYCLE IN C HLAMYDOBAC TE RI A AND 

 CAULOBACTERIA 



(15, 20, 21, 28) 



In chlamydobacteria, such as the filamentous, iron bacterium Sphaerotilus 

 discophoms, as in the case of streptomyces, the organism is essentially sessile 

 and multicellular, so that it must be provided with a distributive mechanism 



