I Found the Entwives!

[Lalwendë]

Well, here's the two sections I think might be the likely candidates:

Many great trees grew there, planted long ago, falling into untended age amid a riot of careless descendants; and groves and thickets there were of tamarisk and pungent terebinth, of olive and of bay; and there were junipers and myrtles; and thymes that grew in bushes, or with their woody creeping stems mantled in deep tapestries the hidden stones; sages of many kinds putting forth blue flowers, or red, or pale green; and marjorams and new-sprouting parsleys, and many herbs of forms and scents beyond the garden-lore of Sam. The grots and rocky walls were already starred with saxifrages and stonecrops. Primeroles and anemones were awake in the filbert-brakes; and asphodel and many lily-flowers nodded their half-opened heads in the grass: deep green grass beside the pools, where falling streams halted in cool hollows on their journey down to Anduin.

Presently, not far ahead, looming up like a black wall, they saw a belt of trees. As they drew nearer they became aware that these were of vast size, very ancient it seemed, and still towering high, though their tops were gaunt and broken, as if tempest and lightning-blast had swept across them, but had failed to kill them or to shake their fathomless roots.

Though I must admit I can't yet see the joke or riddle in there!