Oak

If any plant and planet pairing in this material has a genuine ancient pedigree rather than a Renaissance one, it is the oak and Jupiter.

The oracle at Dodona in Epirus was sacred to Zeus and was read in the sound of a great oak, the rustling of its leaves, and in some accounts the sound of bronze vessels hung in its branches. Homer refers to it in the Odyssey, Herodotus gives an account of its foundation, and it is among the oldest oracular sites in the Greek world, with archaeological evidence of cult activity well before the classical period. The oak is Zeus's tree in Greek cult before anyone drew up a table of planetary rulerships, and Jupiter is Zeus.

The pattern repeats outside Greece without needing to be borrowed. The oak is Thor's tree in Germanic religion, Donar's Oak, felled by Boniface at Geismar in the eighth century as a demonstration that the god would not defend it, and Perkunas's in Baltic religion, and Perun's in Slavic. All of these are thunder gods, and all of them are attached to the oak.

There is a plain physical reason for the convergence, and it is worth stating because it explains the whole cluster. Oaks are struck by lightning disproportionately often: they are tall, often stand isolated in open ground, and their deep-fissured, water-holding bark conducts a strike destructively rather than flashing over. A tree that is visibly and repeatedly hit by lightning attracts a thunder god. Culpeper later repeats the Jupiter attribution, but here he is reporting something far older than himself.

Almost everything popularly known about druids and oaks rests on a single passage, and it is worth reading rather than repeating.

Pliny the Elder, in Book 16 of the Natural History, describes Gaulish priests holding nothing more sacred than the mistletoe and the tree that bears it, provided it is an oak; says they call the mistletoe by a name meaning all-healing; and describes a ritual on the sixth day of the moon in which a white-robed priest climbs the tree, cuts the mistletoe with a golden sickle, catches it in a white cloth, and two white bulls are sacrificed. Pliny also offers the etymology of druid from the Greek drus, oak, which is linguistically doubtful.

That is the source. It is one paragraph, written in Rome by a man who had not seen it, about a people the Romans were conquering, and it is the only detailed classical account of a druidic rite involving oaks. Julius Caesar in the Gallic War describes druids at some length and does not mention oaks or mistletoe at all.

Ronald Hutton has traced in detail how this paragraph was inflated into the elaborate druidic religion of eighteenth- and nineteenth-century antiquarianism, and how little of that construction has any evidential basis. Golden sickles are archaeologically implausible; gold is too soft to cut with. The oak groves, the white robes and the mistletoe of modern druidry descend from Pliny by way of the Romantic revival, not from an unbroken tradition.

The oak's importance to Iron Age Europe is not in doubt. The specific ritual content usually attached to it is one sentence, heavily embroidered.

The oak's standing in northern European culture is best explained by what it did rather than by what it meant, and the practical account is more impressive than the symbolic one.

Acorns fed pigs. The right to run swine in oak woods, pannage, was a valuable and legally defined property interest recorded in Domesday Book, where woodland is measured not by area but by the number of pigs it would support. Acorns were also eaten by people in hard years across Europe and as a staple in parts of the Mediterranean and, more extensively, in Native California, where several peoples ground and leached acorn meal as a principal food. The leaching is essential: acorns are high in tannins and are unpalatable and mildly harmful without it.

Timber built ships and roofs. Oak is strong, durable, resists rot when wet, and can be cleft along the grain into curved pieces that follow the shape of a hull, which is exactly what a wooden warship needs. The naval demand was enormous and shaped forestry policy in England, Spain and France for centuries.

Tannin from oak bark tanned leather, which was a major industry, and oak galls, growths induced by gall wasps, supplied the iron gall ink in which most European manuscripts and records from the medieval period to the nineteenth century were written. Nearly every surviving document of the period is written in a solution made from a tree parasite.

Culpeper used the bark, leaf and acorn as astringents, which is straightforwardly what a high-tannin material does.