Dickinson begins mid-shrug. "Flowers -- Well -- if anybody" sounds like someone interrupting herself in conversation, and the dashes make the thought move forward in small, hesitant steps. It is a challenge: if anyone can explain the "ecstasy" that flowers cause, she will pay up. The feeling she describes is strange, though. It is "Half a transport -- half a trouble." A transport is a rapture, a carrying-away of the self, while trouble is its opposite. Flowers deliver both at once, and the verb she picks, "humble," makes their beauty feel faintly like a reproach.
That is the poem's central idea: beauty is not simply pleasant, and nobody can say why it pulls in two directions. Her image for this is a "fountain / From which floods so contra flow." The Latin prefix in "contra flow" suggests currents running against each other, as if one spring fed joy and pain down opposite channels. The prize she offers is "all the Daisies / Which upon the hillside blow" ("blow" here means bloom). It is a joke, and a neat one. The reward costs her nothing, she could hardly hand it over, and it is the very thing the winner would have explained. The wager is safe because she doesn't expect anyone to collect.
The second stanza turns from challenge to confession. "Too much pathos in their faces" makes the flowers into small, upturned faces that seem to plead with the viewer, and the speaker cannot cope with it. She calls herself a "simple breast," a modest pose that sits oddly beside the sophistication of the poem itself. Then comes the comic swerve. "Butterflies from St. Domingo" are well-travelled visitors, and they are "Cruising," a word that makes them sound like ships, or like tourists strolling without a care. The "purple line" they cruise around is left unexplained. It could be a rim of blooms or a distant horizon, and the poem lets us picture either. These insects "Have a system of aesthetics," which turns them into philosophers with a worked-out theory of beauty. Their system is "Far superior to mine."
The joke has an edge. The butterflies handle flowers lightly and never seem troubled by them, while the speaker is overwhelmed. By the measure of "system," she loses. But the poem suggests, without saying so, that her helpless double feeling may be the more honest response, and that a tidy theory of beauty might be a way of not feeling it. That is an inference from the tone, since she calls her own response inferior and never defends it. The irony lies in the gap between what she says and what the poem makes us believe.
The form supports this. The lines are short, roughly seven syllables, with a falling, trochaic lilt, and the dashes break them into gasps and afterthoughts. The rhyme is sparse and uneven. The first stanza's real rhyme is "flow" and "blow," and the second's is "mine" and "line." That leaves the poem unfinished-sounding, as though it had lost patience with neatness. The word "mine" ends the poem twice over, and it also echoes "define" from line two. The poem begins by asking someone to define the feeling and ends with the speaker conceding her own limits. The last line is the shortest, and it falls flat like a shrug.
Dickinson, who lived in Amherst, Massachusetts, and left most of her poems unpublished when she died in 1886, often built large questions out of small, close-up things, and a flower is about as small as a subject gets. Here a daisy raises one of the hardest questions there is: why does beauty hurt, and why can't we explain it? The poem's answer is characteristically playful. It offers a hillside of daisies for an explanation, keeps the prize, and lets the butterflies drift off with their theories.