A passing glimpse

I never see this growing without thinking of the mention by Robert Frost in this poem:

A Passing Glimpse

To Ridgely Torrence
On Last Looking into His 'Hesperides'

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 it glimpses only to those
Not in position to look too close.