editingNodes.add(node);
  protected void removeChildren(Experiment experiment) {    DefaultMutableTreeNode expNode = findNode(experiment);    int n = expNode.getChildCount();    // display these nodes in gray and don't let them be edited    for (int i = 0; i < n; i++) {      DefaultMutableTreeNode node =         (DefaultMutableTreeNode)expNode.getChildAt(i);      editingNodes.add(node);      model.nodeChanged(node);    }  }