So, here's another of Tolkien's late thoughts that show how deeply he considered each aspect of his subcreation that drew his attention during his late metaphysical writings in which he tried to work out how everything worked. This one is particularly fitting, given how it deals with something that he made iconic in his works:* the nature of trees.
[Something] which distinguishes the living from the unliving** is that the living employ Time in their realization. In other words it is part of their nature to 'grow', using such material as is needed or is available to them for their embodiment. So that a living pattern does not exist fully at any one moment of time (as do unliving patterns); but is complete only with the completion of its life. It cannot therefore rightly be seen instantly, and is only imperfectly envisaged even with the help of memory. Only thosewho conceived its pattern and whose sight is not limited to the succession of time can, for instance,see the true shape of a tree.
Comments on 'The Converse of Manwëwith Eru'
(pages 112 & 114; emphasis mine)
* "In all my works I take the part of trees"—JRRT, 1972 (Letters.419)
**e.g., an 'unliving' material such as iron