LICHENS 



27 



spots; tough when damp, but brittle when dry; odor slight; taste 

 mucilaginous and bitter. For illustrations consult Kraemer's 

 "Applied and Economic Botany." 



Inner Structure. Sections through an apothecium show the 

 hymenium with their asci each containing 8 ascospores and 2 para- 

 physes beneath which is distributed the hypothecium composed of 

 fungal hyphse; an algal layer in the middle subtended by a medullary 

 layer of loose fungal hyphse and a lower or ventral surface composed 

 of several rows of small compactly arranged cells. Tunmann has 

 been able to obtain from small pieces of thallus microsublimates con- 

 taining crystals of lichenostearic acid. (Fig. 10.) 



FIG. 10. Crystals of lichenostearic acid obtained by micro-sublimation of pieces 

 of the thallus of Cetraria, not larger than 0.5 cm. square, a, crystals ob- 

 tained by sublimation; 6, a granular sublimate which was recrystallized 

 from alcoholic solution; c, sublimate treated with sodium carbonate and 

 showing crystal aggregates of the sodium salt of lichenostearic acid; 

 sublimate treated with ammonia giving crystals of the ammonium salt of 

 lichenostearic acid. After Tunmann, Apoth. Zeit., 1913, p. 892. 



Constituents. The principal constituents are lichenin and isolich- 

 enin (about 70 per cent), the former of which appears to be inter- 

 mediate between starch and cellulose, and is soluble in hot water, the 

 solution becoming gelatinous on cooling, but not colored blue with 

 iodin; isolichenin (dextrolichenin) somewhat resembles soluble 

 starch, being soluble in cold water and giving a blue reaction with 

 iodin. The drug also contains 2 to 3 per cent of a bitter crystalline 

 principle, cetrarin, which is colored blue with concentrated hydro- 

 chloric acid and yields on hydrolysis cetraric acid, which is also 

 intensely bitter; 1 per cent of a tasteless, crystalline principle, licheno- 



