A lichen which is discovered in almost every zone of altitude and latitude, which ranges from the wild shores of Melville Island in the Arctic to those of Deception Island in the Antarctic circle,--which blooms on the crests of the Himalayas, on the lofty peak of Chimborazo, and was found by Agassiz near the top of Mont Blanc,--is the _Lecidea geographica_, a beautiful bright-green lichen, whose clusters assume almost a kaleidoscopic appearance. A lichen of great importance in the Arctic world is the well-known _Cladonia rangiferina_, or reindeer moss, which forms the staple food of that animal during the long Arctic winter. In the vast tundras, or steppes, of Lapland it flourishes in the greatest profusion, completely covering the ground with its snowy tufts, which look like the silvery sprays of some magic plant. According to Linnæus, it thrives more luxuriantly than any other plant in the pine-forests of Lapland, the surface of the soil being carpeted with it for many miles in extent; and if the forests are accidentally burned to the ground, it quickly reappears, and grows with all its original vigour. These plains, which seem to the traveller smitten with the curse of desolation, the Laplander regards as fertile pastures; and here vast herds of reindeer roam at will, thriving where the horse, the elephant, and even the camel would perish. This useful animal is dependent almost entirely on a lichen for support. What a deep interest is thus attached to it! That vast numbers of families, living in pastoral simplicity in the cheerless and inhospitable Polar Regions, should depend for their subsistence upon the uncultured and abundant supply of a plant so low in the scale of organization as this, is, says Dr. Macmillan, a striking proof of the great importance of even the smallest and meanest objects in nature.