in Thoreau’s Journal

The surface of the water is the place to see the Pontederia from, for now the spikes of flowers are all brought into a dense line—a heavy line of blue a foot or more in width—on one or both sides of the river. The pontederias are now in their prime—there being no withered heads, they are very freshly blue. In the sun when you are looking west they are of a violaceous blue.