code: function get_highest_val (node, prop) {
      var highest = 0;
      node.apply(function (n) {
          if (species_data[n.node_name()] === undefined) {
              return;
          }
          var val = parseFloat(species_data[n.node_name()][prop]);
          if (val > highest) {
              highest = val;
          }
      });
      return highest;
  }
docs: Helper function to get the lowest value in the subnode -- this is used in the sort cbak