298 BULLETIN OF THE TORREY BOTANICAL CLUB [VoL. 91 in making long-term predictions of. biospherie contamination. The problems of major concern in radioecology are those dealing with the fate and biological consequences of fallout materials after they are deposited in the biosphere. Movement of fallout materials in terrestrial ecosystems*. The fallout in a given land area may be deposited directly on soil, plants, or animals (Figure 5), These materials may be redistributed by environmental processes and/or by organisms. They become parts of the ecosystems in which theyare deposited and maybe incorporated in a variety of biogeochemical cycles. ATMOSPHERE pe = aan=ere DECAY ORGANISMS INPUT => OUTPUT ==>: MAJOR — ---+» MINOR Fig. 5. Principal pathways of fallout materials transfer in a terrestrial ecosystem, Most of the current research effort in radioecology (AIBS 1962) is devoted to studies of the oceurrence, redistribution, and cycling of radionnuclides in various kinds of escosystems. In connection with fallout, the general objectives of these studies are: (a) to determine the properties and relative distribution of fallout particles as they are initially deposited on soils, plants, and animals, (b) to evaluate the biotic and abiotic faetors which influence rates of radionuclide redistribution and cycling by different routes of transfer, and (c) to develop and test mathematical models for predicting, on the basis of data available immediately after contamination, the probable *“Any area of nature that includes living organisms and nonliving substances inter- acting to produce an exchange of materials between the living and the nonliving parts is an ecological system or ecosystem.” Odum (1959),