In Slavery in Massachusetts, Thoreau writes:
But it chanced the other day that I scented a white water-lily, and a season I had waited for had arrived. It is the emblem of purity. It bursts up so pure and fair to the eye, and so sweet to the scent, as if to show us what purity and sweetness reside in, and can be extracted from, the slime and muck of earth. I think I have plucked the first one that has opened for a mile.
What does for a mile mean in this sentence? I looked up for in a dictionary, and methinks the author might mean the first lily that he came across, and that was opened, after walking a mile. Or does Thoreau mean something else here?