[Gk. leichen.] These are flowerless plants, without separate stems or leaves, found on rocks, trunks and branches of trees, walls and fences, and on barren soil. They are common everywhere and at all levels, many of them growing on mountain sides to the verge of perpetual snow. Lichens have no roots, but grow by receiving moisture through all parts of their surface. They contain a kind of starch, a bitter substance, a resin, and various coloring matters. They yield rich dyes of various colors, some of which are used in dyeing silks. Iceland moss is a lichen which grows in the most barren parts of Iceland and other cold countries, and is used for food and medicine. The reindeer lichen, covering the barren plains of Lapland and Siberia, is the chief food of the reindeers ; and at one time, when grain was very scarce in Sweden, this lichen was ground up with flour to make bread. The tripe de roche is a lichen growing in the northernmost parts of North America, which the inhabitants there eat mixed with the roe of fishes. (See Moss.)