Saxon countries in the Middle Ages a hole formed by two branches of a
tree growing together was esteemed of highly efficacious value.

On the other hand, we must not confound the spiritual vitality ascribed
to trees with the animistic conception of their being inhabited by
certain spirits, although, as Mr. Tylor[16] remarks, it is difficult at
times to distinguish between the two notions. Instances of these tree
spirits lie thickly scattered throughout the folk-lore of most
countries, survivals of which remain even amongst cultured races. It is
interesting, moreover, to trace the same idea in Greek and Roman
mythology. Thus Ovid[17] tells a beautiful story of Erisicthon's impious
attack on the grove of Ceres, and it may be remembered how the Greek
dryads and hamadryads had their life linked to a tree, and, "as this
withers and dies, they themselves fall away and cease to be; any injury
to bough or twig is felt as a wound, and a wholesale hewing down puts an
end to them at once--a cry of anguish escapes them when the cruel axe
comes near."

In "Apollonius Rhodius" we find one of these hamadryads imploring a
woodman to spare a tree to which her existence is attached:

"Loud through the air resounds the woodman's stroke,
When, lo! a voice breaks from the groaning oak,
'Spare, spare my life! a trembling virgin spare!
Oh, listen to the Hamadryad's prayer!
No longer let that fearful axe resound;
Preserve the tree to which my life is bound.
See, from the bark my blood in torrents flows;
I faint, I sink, I perish from your blows.'"