in Thoreau’s Journal:

Not only the foliage begins to look dark and dense, but many ferns are fully grown, as the cinnamon and interrupted, perfectly recurved over the bank and shore, adding to the leafy impression of the season. The Osmunda regalis looks later and more tender, reddish-brown still. It preserves its habit of growing in circles, though it may be on a steep bank and one half the circle in the water.

The new leaves are now very fair, pure, unspotted green, commonly more or less yellowish. The swamp white oak leaf looks particularly tender and delicate. The red maple is much harder and more matured. Yet the trees commonly are not so densely leaved but that I can see through them; e. g., I see through the red oak and the bass (below Dove Rock), looking toward the sky. They are a mere network of light and shade after all. The oak may be a little the thickest. The white ash is considerably thinner than either.

The grass and foliage are particularly fresh and green after the two days of rain, and we mark how the darkening elms stand along the highways. Like wands or wreaths seen against the horizon, they streak the sky with green.