262 THE PLANT WORLD. 



not drive out the lichens so effectually at the north, so that the 

 " reindeer moss " and some other lichens literally cover large 

 areas as do the grasses in other places. Some suggestion of this 

 wonderful lichen growth may be seen in northern Minnesota, 

 Michigan and Wisconsin, where patches of such lichens may be 

 found covering an acre or more of ground, and in more northern 

 regions, both in America and Europe, the reindeer and other wild 

 and domestic animals depend more or less upon these lichens for 

 their food supply. 



Lecanora esc id cut a grows loosely attached to the rocks in high 

 places in northern Africa, is carried long distances by the wind, 

 and falling in areas where food is scarce, is eaten b}^ the inhabi- 

 tants, both man and lower animals. This species is supposed to 

 have been the manna of the children of Israel. Nor is this the 

 only lichen commonly eaten by man, for Cetraria islandica, a 

 plant found in northern United States, forms an important part 

 of the food of the people of Iceland, and is eaten also by their 

 domestic animals. This plant is especially rich in the peculiar 

 starch-like compound so commonly built up in lichen tissues. Also 

 some of our Gyrophoras and other common lichens as Rainalina 

 calicaris, Parmelia physodes, Pcltigcra canina, and Evernia prit- 

 nastri have been used for food by man. From some of these 

 and certain other lichens may be extracted a substance very like 

 gum-arabic. The nutritive qualities of the lichens is due mainly 

 to the lichenin or starch-like material already mentioned as being 

 built up in the processes of nutrition. But there is a bitter sub- 

 stance also found in lichen tissues, which often gives an unpleasant 

 taste and is irritating to the digestive tract. This may be removed 

 by thorough washing in water or some alkali, when the plants 

 may usually be eaten with impunity. Arctic explorers, northern 

 hunters and trappers, the inhabitants of such countries as Lap- 

 land, Labrador, Greenland, Iceland, Norway, Sweden and Fin- 

 land, as well as travelers in the deserts of Africa, are very glad 

 to have such food for themselves and their domestic animals. 

 When grains or potatoes are at hand, the lichens may be pow- 

 dered and mixed with these articles of food, and a very palatable 

 bread may thus be made ; or the bitter principle may be removed 



