"A passing glimpse" - a poem by Robert Frost

"I often see flowers from a passing car

That are gone before I can tell what they are.

I want to get out of the train and go back

To see what they were beside the track.

I name all the flowers I am sure they weren't;

Not fireweed loving where woods have burnt--

Not bluebells gracing a tunnel mouth--

Not lupine living on sand and drouth.

Was something brushed across my mind

That no one on earth will ever find?

Heaven gives its glimpses only to those

Not in position to look too close."