One thing's for sure: "Shine, Perishing Republic" does not sound like Grandpa's favorite patriotic song. The stars and stripes have seen better days than this "thickening center" that's moldy and corrupt. At times the poem sounds just plain gross, what with all those molten centers and gooey bubbles, and other times it sounds scary like that monster that's about to devour a bunch of cities (yipe). Maybe we feel shocked by such jarring imagery, maybe we're not surprised, but we still can't help but feel a little disturbed by the sound of those bubbles popping to no avail. The speaker needs to use such strong-sounding imagery to get his point across that this decay isn't something to brush off and forget about. Nestled in between it all are moments that sound not so gross and scary but rather serene and sublime (like the alliterative "sadly smiling" in line 3), as if the scary and gross stuff is something we have to accept.
This phrase, in fact, adds to the speaker's somewhat melancholic, somewhat complacent voice. It may not be a happy smile but at least the speaker isn't sounding totally depressed or grossed out by America's decaying empire. The sound of his sad smile makes us feel like that's all we can really do when it comes to this sort of cultural pattern. Accept it, move on, and let's hope that republic still has a shine to it. And we get all that on a sonic level, too.
Moving along with our mind's ear (if you can picture that), the second stanza is all about nature and her cycles, which the speaker uses as a sort of consolation for the apocalypse he sees happening:
the flower fades to make fruit, the fruit rots to make earth.
Out of the mother; and through the spring exultances, ripeness and decadence; and home to the mother. (3-4)
We know you feel better now. Notice again that alliteration? The repeated F sound links the flower to the fruit that later returns to Mother Earth. The "out of the mother" that later becomes "home to the mother" makes these cycles sound all the more natural in the way the speaker uses parallelism to connect it all. So it's not as if this apocalypse came out of nowhere without any rhyme or reason. The decadence of America's republic came and went and now has entered into a state of decay that's all totally normal and part of a natural cycle. And to think simple things like alliteration and parallelism helped to make that connection more apparent to us. Hooray for literary devices, are we right?