The Doctrine of Signatures is an interesting concept of Jakob Bohne’s. He had a mystical vision that the creator put a sign on all things so that we could easily recognize their meanings.
Paracelsus continued this line of thinking by asserting that plants had a likeness to a particular body part, organ, or aspect of the body and this is where the plant would have an effect……. believing that function followed form and that like cures like. An example is seaweed bladder-wrack, used in hypothyroidism. The two bladders hanging down into a V shape look exactly like an enlarged thyroid gland. Pam Montgomery, Plant Spirit Healing.
Look at the flower below of eyebright… at http://www.flickr.com/photos/jfpics/2723140019/ also called euphrasia. See the eyes?