308 BULLETIN OF THE TORREY BOTANICAL CLUB [Von, 91 In this and in other contaminated areas which were serially sampled, the average tissue burdens 7 months after fallout were slightly higher than precontamination background levels. During the same period of time, the concentration of radiostrontium in the bones of animals living in contaminated environments may have increased from two to five times the background concentration. I —— TOTAL RADIOSTRONTIUM o | ai $ ° } dis/min/gm BONE ASH wn oO I RESIDUAL ENVIRONMENTAL CONTAMINATION: MR/HR BETA-GAMMA 0.42 0.33 0.18 9.09 9.0 0.0l II + RADIOSTRONTIUM 20-- 0 ! 1 lOO 200 MILES | 300 | 400 FROM GROUND ZERO Fig. 10. Radiostrontium in bones of jack rabbits collected 6 months after fallout in midline areas 20 to 425 miles from ground zero. From Lindberg et al. (1959). In general, the radioactivity of animaltissues collected a few days after fallout (Figure 8) decreases with increasing distance from ground zero. In two cases (Figure 9) the thyroid activity of kangaroo rats and jack rabbits was found to be higher at a distance of 60 miles from ground zero than at distances of either 12 or 160 miles. Six months after fallout (Figure 10), the maximum coneentration of radiostrontium in the bones of jack rabbits was found to oceur at a distance of 130 miles from ground zero. The concentration of Sr-90 in the bones of animals collected at a distance of more