"the mullioned windows reflecting the green lawns and the terrace"
'Old Mullions', Honington, Warwickshire
Creative Commons Attribution Share Alike'Old Mullions', Honington, Warwickshire - Credit: John Brightley

A mullion is a vertical section which divides up an area of window, a door or a screen. Traditionally, in large country houses the mullions would be made of stone. The stone mullions of Milton Hall (the model for Manderley) may be seen by clicking on the link.

 

Mullioned windows at St Bartholomew the Great, London
Creative Commons Attribution Share AlikeMullioned windows at St Bartholomew the Great, London - Credit: Mike Quinn