The lichens are tough. They can endure extreme contrasts in temperature, and hang on in barren areas where other plants could not get a foothold. In fact, they are pioneers of millions of years’ service. They prepared the way for all the changing elaboration of plants with leaves and stems that followed them, after they had broken down bare rock with their acids, dissolved it, cracked it, and combined their own dead materials with the rock particles to form soil. In these round-edged plates of lichen that cover rocks or tree trunks in the bare February woods, I see a life that is almost independent of the season. It goes beyond or behind our immediate knowledge of it into a kind of primal security, settling in where little else is possible. The color of lichens is the color of the green algae of the sea and of fresh-water ponds. If their blue-grays, gray-greens, or yellows, bring up the cast-steel color of ocean barrens to my imagination, or green water lolling at the sand’s edge, or underwater depths running with fish and shafts of light, there is knowledge to back me up. The progenitors of the lichens and their relatives the mosses--this richly green hair-capped moss that soaks up melting snow in the sunlight--were unicellular organisms that formed in the sea. The line is direct. The algae in lichens need water. Without it they would not be able to make food or reproduce. (The blue-green algae, which as a species is abundant in both marine and fresh waters, as well as in the soil, has the ability of lichens to endure very difficult environments. It can exist in icy pools or hot springs. The latter extreme was brought home very forcibly to me not long ago in Nevada, when I saw this plant growing at the edge of a fissure from which hydrogen sulphide gas was puffing out. The algae was growing where steam condensed near the surface and must have been thriving in temperatures of nearly 200 degrees Fahrenheit.) The color of our inland lichens and mosses changes with the rate of moisture. Reindeer moss withdraws in dry months as a method of coping with a disadvantageous season, instead of trying to carry on an uncertain battle for existence. It shrinks, in other words, turning dry and crunchy underfoot, but in wet weather it absorbs, almost drinks up, water, and then turns spongelike and its color gleams more richly. In the absence of leaves filtering the sunlight, the trunks of the larger oaks are dappled and spotted with these colors of watery origin. I say the larger oaks because the lichens once started may take a long time to spread. The golden lichen is a very slow-growing species, although there are many stone walls in this region that are covered with it. I have watched one spot of golden lichen for two years or more. No bigger than a fifty-cent piece, it grows on a stone step outside the house, and has hardly expanded at all.