Which part of the harmonium vibrate to produce sound?

Dear Student,
Please find below the solution to the asked query:
&nbm is a reed organ. It produces sound when air is passes through brass reeds. When air blows in the air vessels (reed), sound notes are produced.

Hope this information will clear your doubts about the topic.
If you have any more doubts just ask here on the forum and our experts will try to help you out as soon as possible.
Regards