-18- exchangeability of cesium, total amount of root surface available during the wet as compared with the dry season, and increasing acidity of the soil on drying .-° More complete series of radiochemical determinations of the radioisotopes in both plants and soils are needed to understand the mechanisms involved. Contrary to results reported on relative availability of cesium and strontium to plants in other soils, cesium appears to be more readily available than strontium in the atoll island so11.°1-®5 The short half-life tsotopes that contributed to the activity in the muscle during the first 150 days are not known. The rate of decline during this period was approximately the same as the rate of decay for mixed fission products. Radiocesium content of hermit crab muscle is about 1.5 times that in plants (1,000 d/m/g : 700 d/m/g) on a wet weight basis. The radiocerium levels in the soil were too low (<1% of the total activity) to be detected by the radiochemical methods used. Hepatopancreas ("liver") The rate of decline of activity of the hepatopancreas or "liver" of the crab during the first 175 days post-Nectar is not significantly different from the rate of decay of mixed fission products. This is true despite the fact that there was a pre- existing level of long-lived activity approximately equal to the level existing 537 days post-Nectar. gr99| csi37, and Celt4 were found. Equilibrium must be quickly reached and maintained at & constant level proportional to the availability of the long-lived oe yd per se