“On hearing a Symphony of Beethoven” by Edna St. Vincent Millay

What literary device is used in line 10, “the tranquil blossom on the tortured stem”?

Six benches were left empty in every ship that evening when we pulled away from death. and this new grief we bore with us to sea: our precious lives we had, but not our friends. no ship made sail next day until some shipmate had raised a cry, three times, for each poor ghost unfleshed by the cicones on that field.