plants, the algae contribute to the food supply of animal populations. Minerals as well as organic materials, concentrated and incorporated into the algae, are passed on in the food chain to the animals that feed upon them. Thus the radioactive materials pass through the algae to the animals in the normal course of food gathering. The affinity of algae for some of the radioisotopes is well known. For example, Asparagopsis, a marine alga found on the reefs at Bikini and Eniwetok, has a great affinity for iodine (Palumbo, 1955 ). In the presence of yi31 Asparagopsis becomes radioactive. This alga is a succulent morsel sought by fishes; thus the 1131 passes to the fish and along the food chain. The land plants of the tropical islands of the Pacific atolls become contaminated with radioactive materials in two ways: (1) by fallout of material from the air or from the rain water with direct absorption through the leaves, and (2) by absorption from the soil. The soils of the atolls are generally deficient in potassium. deficiency speeds the uptake of Cs137 by the plants. This Although Cel 44 is present in the soils it is so firmly bound there that little is available to the plants. The radioisotopes remain concentrated in the top two inches or less of soil. The rooting habits of the plants, therefore, are associated with uptake of the radioisotopes. The plants with feeder roots close to the surface thus take up more of the radionuclides than do those with deeper root systems. While all of the tissues ofthe plants may contain radioisotopes, the