Upton Long Island New York. Plants growing in the gamma greenhouse at Brookhaven National Laboratory. The plants are arranged in concentric rings around the radioactive Cobalt 60 source which is in the pipe extending into the floor. The source with an activity of 7.5 Curies can be raised or lowered by remote control. While the source is up, the plants receive a continuous dosage of gamma radiation which varies in intensity depending on the distance from the source. When the source is down in its protective shield below the concrete floor the greenhouse can be safely entered for making observations and tending to the plants.