SINCE THE EARLY DAYS OF MICROBIOLOGY IT HAS BEEN KNOWN THAT, during their life cycles, microorganisms exhibit developmental changes in common with other organisms. In the last decade interest in this aspect of microbiology has developed greatly, and research findings have provided an understanding of the genetic, molecular and biochemical bases of development. An important stimulus in this research has been the realis- ation that microbial development, in its various forms, provides interest- ing model systems that have relevance to a much wider understanding of the developmental processes in...