in Thoreau’s Journal:

Trees generally are now bursting into leaf.  The aspect of oak and other woods at a distance is somewhat like that of a very thick & reddish or yellowish mist about the evergreens— In other directions the light graceful—& more distinct yellowish green forms of birches are seen—& in swamps the reddish or reddish brown crescents of the red maple tops—now covered with keys— Oak leaves are as big as mouse ear & farmers are busy planting.