Maize
Surrounding a window are carvings of maize or Indian Corn
The presence of this plant carving in the Chapel raises many questions: not only is it an exotic plant but it originates from North America, a country traditionally thought to have been discovered by Columbus in 1492, almost 50 years after Rosslyn Chapel was built. Lucifer
All it shows is that the sculptors loved their John Barleycorn. It probably brought them closer to God.