high as 16.2 were used, whereas for the decay factor of only 1.02 was used. last collection a The counts for the 1956- 1957 samples, which were not corrected for decay, sented in the appendix tables. are pre- The levels of radioactivity for plant tissues other than scorched leaves are based on wet tissue weights; basis to convert the latter values to a wet weight it is necessary to divide them by 6, dry to wet ratio for this based on dry weights. pressed in uc/kg; tissue. the approximate The values for soils are All values in the text tables are ex- values in the appendix tables are expressed in thousands of d/m/g/. The rate of decline was plotted on a log-log scale be~ cause of its similarity to the decay curve of mixed fission products. The isotopes present in the samples were indicated by the decay curves but in one soil and four plant samples they were specifically identified by radiochemical analysis*. *Work done by D. J. South '