E. M. Romney

Effect of a chronic exposure to gamma radiation on the shrub Ephedra nevadensis in the northern Mojave Desert

A 33,600 Ci 137 CS source which was differentially shielded to increase the uniformity of the distribution of radiation was set up on a 15-m tower in the center of a 9-ha plot in January 1964 in the Rock Valley area of the northern Mojave Desert. In the spring of 1969 the large majority of 5000 Ephedra nevadensis Wats. shrubs (Mormon Tea) within the plot failed to produce flowers and very little vegetative growth occurred on the species in contrast to a control plot and to other nonirradiated areas. The 5-year cumulative radiation exposure throughout about 85 per cent of the plot ranged from 3·9 to 9·8 kR. Radiation effects on other species were nonexistent or doubtful. E. nevadensis has a higher interphase chromosome volume than do the other shrub species.