Attaching the list
By attaching the list part to the label above it and to the push button below it, you can allow it to fill all the vertical space between those two parts: 
Edge 
Attachment 
Top 
Attachment type: XmATTACHWIDGET 
Offset: 2 
Attached parts: Label3 
Bottom 
Attachment type: XmATTACHWIDGET 
Offset: 10 
Attached parts: Push Button1 
Left 
Attachment type: XmATTACHFORM 
Offset: 10 
Right 
Attachment type: XmATTACHPOSITION 
Offset: 48 
Last modified date: 01/29/2015