WillC said:The dark color around the node is not a good sign. If it is soft and squishy, then it has rotted and it probably will not recover. However, I am surprised that that would happen in just a week. If the black stuff wipes off and it is firm underneath, then keep it in water as you have. Be patient as it will take many weeks for healthy roots to form.
Is there another stem node above the one you have kept in water?