Lucan, the Latin poet, in his _Pharsalia_, refers to the seclusion of the Druids' groves and to their doctrine of immortality.

The Scholiasts' notes on this passage are after the manner of their kind, and add very little to our knowledge.

In Pliny's _Natural History_ (xvi, 249), however, we seem to be face to face with another, though perhaps a distorted, tradition.

Pliny was an indefatigable compiler, and appears partly by reading, partly by personal observation, to have noticed phases of Celtic religious practices which other writers had overlooked.

In the first place he calls attention to the veneration in which the Gauls held the mistletoe and the tree on which it grew, provided that that tree was the oak.