1366 SECTION 12. were very high, especially in the lower leaves, in which Ca ranged from 690 to 980 meq per 100 gm of dry tissue. Analyses of Leaf Tissue Collected on Rongelap Atoll Foliage samples have been collected in the field, primarily from woodyplants, which dominate the atoll environment. In most cases separate samples were taken of the upper and the lower foliage of the plants. Representative values for K and Cs-187 in three of the common species are given in the lower part of Table 1. Potassium contents of the upper foliage have consistently proved to be much higher than those in the lowerfoliage. On the other hand, Ca and Mg levels have been consistently higher in the lower than in the upper leaves. In the case of Cs-137, the pattern is consistent in the samples of a particular species, but there are differences between the species. In Messerschmidia and Pandanus, Cs-137 levels are higher in the upper than in the lower foliage, which is the same pattern that was observed in the squash grown in the greenhouse. In contrast, Scacvola showshigher levels of Cs-137 in the basal than in the upperleaves. In one instance the effect of mineral fertilization in the field was tested. Two 1/80 acre plots in a coconut grove on Rongelap Island were treated with a broad- cast application of KC] in August 1958, at a rate of 140 pounds K;O per acre. The dominant ground vegetation, a grass (Lepturus sp.), was sampled in March 1959 from thefertilized and control areas. Average values for the content of K(meq per 100 dry gm) and Cs-187 (d/m/gm) were as follows: Control—10.1 K, 65 Cs-137; Fertilized—16.5 Kk, 20 Cs-137. Samples from the same locations collected in September 1959 showed no significant difference in either K or Cs contents, however, and so the depressive effect of the K fertilization on Cs-137 was apparently transitory, although the possibility of seasonal differences exists. DISCUSSION N, P, and fertilization in various combinations depressed the uptake of Cs-137 in all cases in the greenhouse experiments. It was clear that dilution by increase of dry yield withfertilization could not explain the reduction of the Cs-137 levels, but no general explanation for the effects of the three elements can be given at this time. One fact of possible interest in this connection was the considerably higher uptake of K which was observed with the P-K treatments (i.e. without N) with both squash and tomato. The results of the pot cultures do not distinguish clearly between the effects of the different fertilizer elements on Cs-137 content of the plants, since no treatments involved single elements. There was an indication in the tomato that high k content was associated with lower Cs-137 content, but this was not confirmed by the tests using squash. A possible explanation for this difference lies in the fact that tomato responded in yield to K additions but squash did not. In the fertihzation with K in the field, at least a temporary depression of Cs-137 uptake was effected. This is consistent with the results of Nishita et af. (1960), who observed a decreased absorption of Cs-137 with K fertilization of soil which was low in K. The Rongelap soils are low in K as evidenced bysoil analyses and by the very lowlevels of K in the older leaves of the plants growing on them. Thedifferences between upper and lower fohage in their content of the various ions are of special interest. The most usua! pattern shows both K and Cs-137 higher in the upper leaves than in the lower leaves. Field-collected Scaecola ™~