A Scribal and Illuminated Rebus?

Among the digitized manuscripts at Villanova University, PA, is a very small (approx.100×70mm) 14th-century English copy of some of Augustine's works, with a single illuminated page at the beginning:

[This and other images: Digital Library@Villanova University; Source]

The thing that strikes me as most unusual about this first page is the lower border, with foliage sprouting from what looks like a hole in the side of a wooden barrel: