Moss grows where nothing else can grow. It grows on bricks. It grows on tree bark and roofing slate. It grows in the Arctic Circle and in the balmiest tropics; it also grows on the fur of sloths, on the backs of snails, on decaying human bones. … It is a resurrection engine. A single clump of mosses can lie dormant and dry for forty years at a stretch, and then vault back again into life with a mere soaking of water.