Henry David Thoreau, Journal
(May 20, 1851):
The most clear and ethereal ideas (Anteus-like) readily ally themselves to the earth, to the primal womb of things. They put forth roots as soon as branches; they are eager to be soiled. No thought soars so high that it sunders these apron-strings of its mother. The thought that comes to light, that pierces the empyrean on the other side, is wombed and rooted in darkness, a moist and fertile darkness,—its roots in Hades like the tree of life. No idea is so soaring but it will readily put forth roots. Wherever there is an air-and-light-seeking bud about to expand, it may become in the earth a darkness-seeking root.
On Antaeus see (e.g.) Apollodorus, Library
2.5.11 (on Heracles, tr. Michael Simpson):
When he learned where they were he traveled through Libya, then ruled by Antaeus, son of Poseidon, who forced strangers to wrestle with him and killed them. Heracles, compelled to wrestle with him, raised him off the ground (for when he touched earth he became stronger, hence was said by some to be a son of earth) and crushed him to death.
On the roots of a tree in Hades, cf. the idea that some trees extend as far under ground as above it, e.g. in Vergil, Georgics
2.290-297 (tr. J.W. Mackail, esp. 291-292):
The tree is sunk deeper and right into the earth; the winter-oak beyond all, who, as high as her top scales the air skyward, strikes her root as deep as hell: therefore not storms nor blasts nor rains uproot her; she abides unstirred, and outlives many children's children, and sees roll by her many generations of men; and stretching wide to right and left her strong boughs and arms, uprears the mass of her own enfolding shade.
altior ac penitus terrae defigitur arbos,
aesculus in primis, quae quantum vertice ad auras
aetherias, tantum radice in Tartara tendit.
ergo non hiemes illam, non flabra neque imbres
convellunt: immota manet multosque nepotes,
multa virum volvens durando saecula vincit,
tum fortis late ramos et bracchia tendens
huc illuc media ipsa ingentem sustinet umbram.