Sir James George Frazer (18541941). The Golden Bough. 1922.
cloud in a flash of lightning, leaving a token of his presence or of his passage in the riven and blackened trunk and the blasted foliage. Such trees would thenceforth be encircled by a nimbus of glory as the visible seats of the thundering sky-god. Certain it is that, like some savages, both Greeks and Romans identified their great god of the sky and of the oak with the lightning flash which struck the ground; and they regularly enclosed such a stricken spot and treated it thereafter as sacred. It is not rash to suppose that the ancestors of the Celts and Germans in the forests of Central Europe paid a like respect for like reasons to a blasted oak.
This explanation of the Aryan reverence for the oak and of the association of the tree with the great god of the thunder and the sky, was suggested or implied long ago by Jacob Grimm, and has been in recent years powerfully reinforced by Mr. W. Warde Fowler. It appears to be simpler and more probable than the explanation which I formerly adopted, namely, that the oak was worshipped primarily for the many benefits which our rude forefathers derived from the tree, particularly for the fire which they drew by friction from its wood; and that the connexion of the oak with the sky was an after-thought based on the belief that the flash of lightning was nothing but the spark which the sky-god up aloft elicited by rubbing two pieces of oak-wood against each other, just as his savage worshipper kindled fire in the forest on earth. On that theory the god of the thunder and the sky was derived from the original god of the oak; on the present theory, which I now prefer, the god of the sky and the thunder was the great original deity of our Aryan ancestors, and his association with the oak was merely an inference based on the frequency with which the oak was seen to be struck by lightning. If the Aryans, as some think, roamed the wide steppes of Russia or Central Asia with their flocks and herds before they plunged into the gloom of the European forests, they may have worshipped the god of the blue or cloudy firmament and the flashing thunderbolt long before they thought of associating him with the blasted oaks in their new home.
Perhaps the new theory has the further advantage of throwing light on the special sanctity ascribed to mistletoe which grows on an oak. The mere rarity of such a growth on an oak hardly suffices to explain the extent and the persistence of the superstition. A hint of its real origin is possibly furnished by the statement of Pliny that the Druids worshipped the plant because they believed it to have fallen from heaven and to be a token that the tree on which it grew was chosen by the god himself. Can they have thought that the mistletoe dropped on the oak in a flash of lightning? The conjecture is confirmed by the name thunder-besom which is applied to mistletoe in the Swiss canton of Aargau, for the epithet clearly implies a close connexion between the parasite and the thunder; indeed thunder-besom is a popular name in Germany for any bushy nest-like excrescence growing on a branch, because such a parasitic growth is actually believed by the ignorant to be a product of lightning.