404 



ECONOMIC AND TECHNICAL 



These lichens are not bitter to the taste, nor are they irritating as are other 

 species of the genus. They are on the contrary quite harmless and are much 

 relished by the Japanese on account of their agreeable flavour, in spite of 

 their being somewhat indigestible. Though only determined scientifically in 

 recent times, this edible lichen has long been known, and the risks attending 

 its collection have frequently been described in Old Chinese and Japanese 

 writings. 



Other species of Gyrophora including G. polyi'hiza (Fig. 129) and 

 Umbilicaria, black leathery lichens which grow on rocks in northern regions, 



Fig. 129. Gyrophora polyrhiza Koerb. (.S.H., Photo, reduced). 



have also been used as food. They are the "Tripe de Roche" or Rock Tripe 

 of Arctic regions, a name given to the plants by Canadian fur-hunters. 

 They have been eaten by travellers and others in desperate straits for food ; 

 but though to a certain extent nutritious, they are bitter and nauseous, and 

 cause severe internal irritation if the bitter acids are not first extracted by 

 boiling or soaking. 



Of more historical interest is the desert lichen Lecanora esculenta, 

 supposed to be the manna^ of the Israelites, and still called "bread from 

 heaven." Eversmann^ wrote an account of its occurrence and qualities, and 

 fuller information was given by Berkeley = : when mixed with meal to a 

 third of its weight it is made into bread and eaten by the desert tribes. 

 It grows abundantly in North Africa and in many parts of Western Asia, 

 on the rocks or on soil. It is easily broken off and driven into heaps by the 

 wind; and has been reported as covering the soil to a depth of 15 cm. to 



^ See p. 422. 2 Eversmann 1825. ' Berkeley 1849. 



