Any branch of biology depends for its progress on the development of new concepts and to a lesser, but sometimes crucial, extent on the elimination of erroneous notions. Understanding the roles of bacteria required first the observation that such minute creatures existed, and subsequently the exper imental demonstrations that their presence was necessary for the occurrence of particular phenomena. In this first volume, the authors review the development of scientific understanding of the role of microbes as agents of diverse natural processes. Notably absent is a separate review of the history of microbes as agents of disease, a his tory available in many other publications. Regrettably absent is a review of the his tory of microbes as agents of inorganic transformations, a serious omission that resulted from the illness of the prospective author late in the preparation of this volume. The topic will of course be treated in later volumes, although not predominantly in a historical manner. Otherwise, the emphasis in this volume is on the history of understanding interrelationships between modes of bacterial existence and the inanimate environment. These relationships were established long be fore multicellular, differentiated or ganisms appeared as potential microbial habitats, and their recognition and elucidation contributed greatly to the widened appreciation of bacterial di versity and the importance of these simpler creatures to the physiochemical conditions of the biosphere.

Volume 2.

The value of studies of monotypic populations is constantly argued in bacterial ecology. The controversy itself is evidenceofthe strong awareness that bacterial activities in natural sites are not determined by the bacteria alone. At the same time, the best evidence that bacteria are influenced by environmental factors is the contrast between their behavior in laboratory cultures and their relatively subdued influence when in the presence of com petitors, predators, and fluctuating-often stressful-environmental conditions. Monotypic populations are admittedly reductionist, but are not therefore irrelevant to bacterial ecology. Quite the contrary. Without pure culture studies, our understanding of important and applicable bacterial activities-N fixation, for example-would still be z limited to what we could discern from a comparison of events in steamed vis-a-vis un heated soil. As was evident throughout the previous volume in this treatise, practically any method of studying natural bacterial communities upsets them while permitting only limited assessment of the respective qualities and quantitative contributions to total com munity activity of each type of bacterium present. Total activity itself is difficult to assess and is not dependably accomplished by any single method. This third volume comprises information regarding the properties of bacteria as they have been learned largely from pure culture studies. Its purpose is twofold: to provide readers with fundamental information regarding the cellular organization, physiological capabilities, and genetic systems of bacteria; and to connect known bacterial properties with environmental influences on them and with their influences on natural processes.