478 PHYSIOLOGY AT THE FAEM. 



turn, variegated rough horsetail. The large proportion of finely- 

 divided silica in horsetails may render them useful in manures. 



Sub-class Thallogence. Musci, Moss order. Spaghnum 

 forms part of the food of the reindeer, and in the polar regions 

 the inhabitants dry it and make it into a sort of bread. 



Lichenes, Lichen order. Cetraria Islandica, Iceland moss, 

 contains starch along with a bitter principle. In Iceland 

 and Lapland it is used as an article of diet, being boiled in 

 broth or milk after being freed from its bitter by repeated 

 macerations in water : it is also dried and made into bread. 

 C. nivalis is also nutritive. Cladonia or Cenomyce rangi- 

 ferina, reindeer moss, the name being appropriate as the vast 

 herds of reindeer in Lapland are supported by it for a great 

 part of the year, and especially in winter. 



GyropJiora includes many species of dark lichens, which 

 have a certain amount of nutritious quality. These are the 

 lichens on which, under the name of tripe de roche, Franklin 

 and his companions lived for many weeks. 



Sticta pulmonacea, lungs of the oak, is used in the diet of 

 invalids. 



Lecanora esculenta and L. affinis sometimes appear in Persia, 

 Armenia, and Tartary, suddenly in immense quantities, and are 

 eaten eagerly by the inhabitants as food from heaven. 



Fungi, Mushroom order. A comparatively small number 

 of mushrooms are accounted edible and safe in this country. 

 Agaricus campestris, with pink gills, is the common edible 

 mushroom of Britain. A. Georgii is another edible British 

 species. A. prunulus is a delicious mushroom, neglected in 

 this country. 



Boletus esculentus, and some other species of boletus, are 

 edible. Gyttaria Darwinii grows on species of beech, and is 

 used as food in Tierra del Fuego. C. Berteroi is a Chilian 

 species, growing on Fagus obliqua, which is also edible. 



