Oak bark (Quercus robur) 
Bark of the pedunculate oak (Quercus robur), scraped from the outer layer and crumbled.
Characteristics
- Oak bark is rich in tannins.
- In biodynamics it is the basis of preparation 505, packed into a domestic animal's skull.
- Only the outer layer is used, finely grated.
Role in the preparation: The crumbled bark is packed into the skull, which is left in a wet place all winter.
Caution: Take it from fallen or cut branches without harming the living tree, and with the owner's permission.
Sources: Quercus robur - Wikipedia · Biodynamic agriculture - Wikipedia
Documentary information: this is neither a recommendation for use nor a plant-protection or veterinary claim. Check your country's regulations before any use.