Irena wrote each child's real name, in code, on thin tissue paper. She made two identical lists and sealed them in jars.
Then she buried them under an apple tree in a neighbor's backyard, right across the street from a German barracks.
The lists were the only way the children could one day be told who they really were. They were also dangerous. "When I once had the list at home," she said later, "that same night the Gestapo arrived."