First steps in biological nitrogen fixation

maries of present day research, it seems worth-while to furnish a perspective of some of the events that led to the modern studies that have been made possible by the development of cell-free systems capable of fixing N2. This contribution will be limited primarily to those steps that are most closely related to the subject matter of the biochemical papers on the programme. This choice is dictated, not only because of the limits of time but also because these papers represent the area of my own research interests and, presumably, then, the area of my greatest competency. Alone, perhaps this would not be enough, but if the personal participation that furnishes background dealing with items of human interest and errors-observations that never get into the published works-is added, it should suffice. Other aspects in the field are represented in the discussion by the contributors of the afternoon portion of the programme; but having heard three of these recently, I am confident that these papers, too, will have a biochemical component. As a convenient point of departure, let us consider the state of the art in 1932 as recorded in the monograph Root nodule bacteria and leguminous plants, by Fred, Baldwin & McCoy (1932). Widely acclaimed by critics for its overall coverage, it represents the type of summary that would not be possible today-at least, not in a volume of 343 pages. Examination discloses that the available biochemical information required few of these pages; aside from some elementary chemical analyses of bacteria and plants, the following are of interest: (a) Mechanism of fixation: 10 pages which included material on both symbiotic