One writes such a story [The Lord of the Rings] not out of...

One writes such a story [The Lord of the Rings] not out of the leaves of trees still to be observed, nor by means of botany and soil-science; but it grows like a seed in the dark out of the leaf-mold of the mind: out of all that has been seen or thought or read, that has long ago been forgotten, descending into the deeps. No doubt there is much personal selection, as with a gardener: what one throws on one's personal compost-heap; and my mold is evidently made largely of linguistic matter.