“Eddie,” he said, “there’s a dark-green notebook on my desk in the study. I forgot it this morning. Can’t get away from here, and I need it.” “I’ll bring it over, Dad,” Eddie volunteered quickly. “Good. I’ll be outside the botany building. Know where that is?” “Botany? Where they raise all the plants and stuff?” Eddie asked. “That’s right.” “I know where it is,” Eddie said. “Be there in five minutes.” He went into the study, got the notebook off the desk, and went back outside. “I’ve got to tear over to school with this notebook,” he explained to Teena. “That was my dad.” “I’ll go with you,” Teena said. “O.K.” It was only a few blocks to the college campus. Reaching the grounds, they took a short cut past the men’s gymnasium, crossed the athletic field, and arrived at the Botany Building. “I see Dad over there,” Eddie said, pointing. There were several men standing in a group in the small cultivated field which the botany department used to grow test plants of various kinds. Eddie and Teena picked their way carefully between the rows. “You made good time, Eddie,” his father said, taking the notebook. “Morning, Teena. Hope I didn’t interrupt any big plans.” “Oh, no, Mr. Taylor,” Teena said. “We weren’t doing anything special.” Eddie was about to turn and leave, when he noticed that several of the young men—students, no doubt—were wearing strange-looking, long, heavy gloves. “Why the gloves, Dad?” he asked. Mr. Taylor glanced up from the notebook. “We’re experimenting with radioactive tracers,” he said. “They’re weak—certainly not dangerous—but there’s no harm in taking a little extra precaution. The gloves are lead-lined and absorb any of the rays which might possibly be picked up from handling the plants.” “What are tracers, Mr. Taylor?” Teena asked. Eddie shot her a quick scowl. He doubted that his father wanted to be bothered with questions at the moment. Then Eddie noticed one of the students holding the wandlike probe—or diode—of a Geiger counter down close to the leaves of one plant. It seemed a strange thing to be doing. Who would prospect for uranium in plants. “That’s a good question, Teena,” Mr. Taylor said. “Glad to see you’re interested.” He turned and spoke to the student with the Geiger counter. “Jim, you want to explain to this young lady, and my son here, what tracers are?” Eddie smiled to himself. His father was the kind of a professor who believed his students should have the chance to use their knowledge whenever possible. “Maybe we should all listen to this,” Eddie’s father said to the others. They gathered around as the dark-haired student switched off the Geiger counter, swallowed a bit uncomfortably, and turned to face the outdoor classroom which Teena’s question had formed on the spot. “Well, er—” Jim began, addressing Teena, “a tracer is a radioactive isotope which we—well, send out on a journey, then follow it with a Geiger counter.”