William Logan in The New Criterion:
As he recalled it,
I got out of a train at, I think, La Concorde and in the jostle I saw a beautiful face, and then, turning suddenly, another and another, and then a beautiful child’s face, and then another beautiful face. All that day I tried to find words for what this made me feel. That night as I went home along the rue Raynouard I was still trying. I could get nothing but spots of colour. I remember thinking that if I had been a painter I might have started a wholly new school of painting. . . . Only the other night, wondering how I should tell the adventure, it struck me that in Japan, where a work of art is not estimated by its acreage and where sixteen syllables are counted enough for a poem if you arrange and punctuate them properly, one might make a very little poem which would be translated about as follows:—
“The apparition of these faces in the crowd :
Petals on a wet, black bough.”
—“How I Began,” T.P.’s Weekly, June 6, 1913
Early in March 1911, Ezra Pound arrived in Paris. By late May he had moved on. The specters in the Métro obviously haunted him. The lines were finished by fall the following year, when he sent Poetry a batch of poems that, he hoped, would “help to break the surface of convention.” When these “Contemporania” were published at the head of the April 1913 issue, the poem appeared in this fashion:
In a Station of the Metro
The apparition of these faces in the crowd : Petals on a wet, black bough .
The first thing striking about the couplet is the subject—beauty discovered underground.
More here.