Dave Bonta looks closely at an oak apple gall, the round growth that forms on an oak tree, and finds a small marvel in something most people would call strange or useless. The poem begins by piling up descriptions: it's a "planet" that happens by accident, a "green anti-fruit" that looks like a citrus but is filled with air, with a larva at its center. The word "bitterness" hints at its sour reputation.
The speaker's tone is curious and admiring rather than disgusted. Comparing the tree's reaction to an oyster walling off an irritant makes the gall seem less like a disease and more like a clever act of defense, even a kind of pearl. The ending is the most striking part. In autumn the gall turns red, doesn't rot, and dries into "tough brown paper," which the speaker calls "a manuscript in the round." That image suggests something written and kept, until it "whelps a wasp." The mood is quiet, observant, and gently surprised by how life emerges from an irritation.