The Morgoth-element.

[Marwhini]

I found the relevant quote dealing with the Ents, Dwarves, elves, etc.:


Morgoth's Ring, pp. 394 - 395, Notes on Motives in the Silmarillion:

To gain dominion over Arda, Morgoth had to let most of his being pass into the physical constituents of the Earth – hence all things that were born on Earth, and lived on and by it, beasts or plants or incarnate spirits, were liable to be 'stained'.

This quote precedes the quote in my OP by one page, with an intervening comparison of the older and newer mythology, and the relationship of Morgoth and Sauron's means of domination.

But it eventually reaches the point where it describes this 'stain' AS the 'Morgoth-element', which is incorporated into the very fabric of existence in Ëa.

MB