The poem is James Merrill's "Lost in Translation," which you can find here, with partial audio. the echo is of Paul Valery's "Palme," which comes up at several points in Merrill's narrative and reflections.
As my former Rebbe (i.e., dissertation director) Stephen Yenser explains:
Merrill has absorbed much of "Palme" in "Lost in Translation," and lines especially relevant to this constellation of puzzle pieces occur in Valery's seventh stanza:More on what's now blossoming from those roots next week.
Ces jours qui te semblent vides
Et perdus pour l'univers
Ont des racines avides
Qui travaillent les deserts.
Merrill quotes Rilke's translation as his epigraph:
Diese Tage, die leer dir scheinen
und wertlos fur das All,
haben Wurzeln zwischen den Steinen
und trinken dort uberall.
And here finally is Merrill's own rendering, published several years after "Lost in Translation":
These days which, like yourself,
Seem empty and effaced
Have avid roots that delve
To work deep in the waste.