[Illustration: _An ecologist inspects cages placed around bagworm infestations of a red cedar tree that had been injected with radioactive cesium-134 to determine uptake of radioactivity in the larvae._] [Illustration: _Checking pine seedlings exposed to ionizing radiation from a radioactive source (on tripod) in a controlled ecosystem. Seedlings on left were fully exposed, those in the middle were exposed on their tops only, and those on the right were exposed on their stems only._] [Illustration: _Biologist studying the root distribution of plants by injecting radionuclides into the soil and measuring plant uptake._] [Illustration: _A thriving_ Messerschmidia _plant growing on Rongelap Atoll is studied for growth-rate and root-systems data after the island was accidentally subjected to radioactive fallout_.] [Illustration: _Aerial view of a “Gamma Forest”, where growing trees are exposed to chronic irradiation from a source at the center of the picture. This environmental biology study shows varying sensitivity of various trees. Trees in the center were killed by extremely high doses of radiation for 20 hours a day over a 6-month period._] [Illustration: _Apparatus containing a strong radiation source being installed by biologists in a semitropical rain forest for terrestrial ecology research._] In programs of such scope and duration, the problems of interpretation are great. Broadly, environmental studies give consideration to: 1. The amounts and kinds of radioactivity released to the environment. 2. The rates of uptake by the biological system. 3. The amounts and kinds of radioactivity within the system. 4. The rates of metabolic transfer or elimination. 5. The amounts and kinds of radioactivity concentrated in tissue and acting internally. 6. The time required for biological processes to be completed and for any biological effects to develop. Biological Inventories Familiarity with the biological components of an ecosystem is essential to meaningful radiobiological assessment. Inventories of natural components were not made in the early nuclear test programs because of inadequate realization of the biological potential. Later, they could be made only after radionuclides already had been introduced into the environments. The survey of the mid-Pacific region before Operation Crossroads represented the earliest effort to examine an environment in detail before a nuclear detonation, but was designed so that it had only inferential value for other long-range biological research. The test surveys were useful, however, in expanding knowledge of specific environments. In addition, it was standard practice to make comparative collections of organisms in regions removed from the test sites to establish base lines, or “controls”, against which to measure radiobiological developments.