Koen, you found an excellent example of the teasel heads in a carding bat.
As a reference to the way the roots are drawn, messy and large (out of proportion to the plant) and not completely covered with brown or red like many of the other roots, uncarded wool looks like this:
Photo courtesy of Laurie, CurlyQ Books
Teasel heads were absolutely essential to wool production as they were used to card the fibers (align the fibers) prior to spinning and, as Koen mentioned, to raise the nap and brush the fabric after it was spun.
Teasel (
Dipsacus) is included in medicinal herbals due to the cleansing properties of the roots.
Also of interest is that one of the names of the plant is "Venus's basin" (which might explain the exaggerated cup shapes) and another is
Virga pastoris (a reference to shepherds' hooks, which might explain the extra "hooks" on the ends of the leaves).
I can't help wondering, assuming this is teasel, whether it is meant to encompass several kinds of teasel. Many herbal compendiums include two or three kinds of teasel. If this is teasel, and if there is only one, then perhaps the cupped leaves represent cut-leaved teasel and the roots represent Fuller's teasel.
Also, many aspects of the VMS strike me as quite focused, quite targeted. If that impression is correct and if this is teasel, then this drawing reinforces that impression. Note how the basal leaves are not included, as they are less important than the parts that are primarily used (heads and roots), and are not needed for identification. For someone familiar with the plant, there is enough information here to identify both the plant and its uses (the cups are mnemonic for the name, the roots are mnemonic for the use). I mention this because there are other VMS plants that seem to me to have this characteristic... of including what is important and leaving out what is not.