A little moisture, a fog, or rain, or melted snow makes his wilderness to blossom like the rose.

February 7. 

Evidently the distant woods are more blue in a warm and moist or misty day in winter, and is not this connected with the blue in snow in similar days? 

Going along the Nut Meadow or Jimmy Miles road, when I see the sulphur lichens on the rails brightening with the moisture I feel like studying them again as a relisher or tonic, to make life go down and digest well, as we use pepper and vinegar and salads. They are a sort of winter greens which we gather and assimilate with our eyes. 

That’s the true use of the study of lichens. 

I expect that the lichenist will have the keenest relish for Nature in her every-day mood and dress. He will have the appetite of the worm that never dies, of the grub. To study lichens is to get a taste of earth and health, to go gnawing the rails and rocks. This product of the bark is the essence of all times.

The lichenist extracts nutriment from the very crust of the earth. A taste for this study is an evidence of titanic health, a sane earthiness. It makes not so much blood as soil of life. It fits a man to deal with the barrenest and rockiest experience. 

A little moisture, a fog, or rain, or melted snow makes his wilderness to blossom like the rose. 

As some strong animal appetites, not satisfied with starch and muscle and fat, are fain to eat that which eats and digests, — the contents of the crop and the stomach and entrails themselves, — so the lichenist loves the tripe of the rock, — that which eats and digests the rocks. He eats the eater. 

“Eat-all” may be his name. 

A lichenist fats where others starve. His provender never fails. 

What is the barrenest waste to him, the barest rocks? A rail is the sleekest and fattest of coursers for him. He picks anew the bones which have been picked a generation since, for when their marrow is gone they are clothed with new flesh for him. What diet drink can be compared with a tea or soup made of the very crust of the earth? There is no such collyrium or salve for sore eyes as these brightening lichens in a moist day. 

Go and bathe and screen your eyes with them in the softened light of the woods.

H. D. Thoreau, Journal, February 7, 1859

Going along the Nut Meadow or Jimmy Miles road, when I see the sulphur lichens on the rails brightening with the moisture. See February 6, 1852 ("Near the C. Miles house there are some remarkably yellow lichens (parmelias?) on the rails, -- ever as if the sun were about to shine forth clearly")

Evidently the distant woods are more blue in a warm and moist or misty day in winter, and is not this connected with the blue in snow in similar days? See  note to February 7, 1856 ("During the rain the air is thick, the distant woods bluish."); see also February 2, 1854; ("The shade of pines on the snow is in some lights quite blue."); February 6, 1854 ("Crossing Walden where the snow has fallen quite level, I perceive that my shadow is a delicate or transparent blue .");  February 10, 1855 ("I go across Walden. My shadow is blue. It is especially blue when there is a bright sunlight on pure white snow."); February 11, 1855 (“The atmosphere is very blue, tingeing the distant pine woods.”);  January 3, 1856 ("The snow turned to a fine mist or mizzling, through which I see a little blue in the snow, lurking in the ruts.") 

They are a sort of winter greens which we gather and assimilate with our eyes. See November 24, 1858 ("It is lichen day."); December 31, 1851 ("Nature has a day for each of her creatures, her creations. To-day it is an exhibition of lichens at Forest Hall.”); January 7, 1855 (“It is a lichen day. . . . How full of life and of eyes is the damp bark!”); January 26, 1852 ("The lichens look rather bright to-day, . . .The beauty of lichens, with their scalloped leaves, the small attractive fields, the crinkled edge! I could study a single piece of bark for hour.”); January 26, 1858 (“This is a lichen day. The white lichens, partly encircling aspens and maples, look as if a painter had touched their trunks with his brush as he passed”); February 5, 1852 ("The stems of the white pines also are quite gray at this distance, with their lichens”); February 5, 1853 ("It is a lichen day. . . . All the world seems a great lichen and to grow like one to-day, - a sudden humid growth.”); March 5, 1852 ("Such is the mood of my mind, and I call it studying lichens. The habit of looking at things microscopically, as the lichens on the trees and rocks, really prevents my seeing aught else in a walk").