262 Mary Davies Sivartz, 



ter only, which yields (i-glucose. The algae investigated are thus all 

 seen to yield pentoses, very frequently fructose and methyl-pentose, 

 sometimes glucose and galactose. 



Lichens are symbiotic forms embracing algae and fungi. Because 

 of this symbiotic nature, they exhibit great variety in composition. 

 From the investigations of Escombe (6), Ulander and Tollens (27), 

 Karl Miiller (11), Nilson (14), Wisselingh (29) and others, i it appears 

 that the cell walls are usually of cellulose, but occasionally of chitin.^ 

 Many species yield on extraction with hot water a gelatinizing sub- 

 stance, which Berzelius (2) in 1808 named " Flechtenstarke " (lichenm), 

 but which later investigators' have shown to be, not a single substance, 

 but a number of related carbohydrates yielding dextrose, such as 

 lichenin from Cetraria and Ramalina fraxinea, and evernin from Ever- 

 nia prunastre, usnin from Usnea harbata. Other species, on the con- 

 trary yield little dextran, but mannan, galactan, pentosan and methyl- 

 pentosan in varying proportions. The table on page 2.57 showing the 

 hemi-celluloses occurring in a number of lichens, has been compiled 

 from data given by Karl Miiller (11) and Ulander and Tollens (27). 



Occurrence and Nature of Cellulose. 



Cellulose is said to occur in pure form in the wall of the young plant 

 cell. With increasing age, modifications take place by which the true 

 cellulose becomes more and more encrusted with lignin and cutin, 

 two substances shown by Konig (52), Fiirstenberg (39), and Murdfield 

 (63) to be almost entirely indigestible. According to Wielen (87) and 

 Hofmeister (43), even pure cellulose is not a simple substance, but can 

 be separated into soluble and insoluble portions."* Much of our in- 

 formation regarding the nature of cellulose is due to the work of 

 Schulze and his pupils. Schulze (75) has defined cellulose as that part 

 of the cell wall giving the typical cellulose reactions,^ and yielding 

 dextrose on hydrolysis with concentrated sulphuric acid. 



^For early literature see Czapek, Biochemie der Pflanzen, Vol. I, pp. 514-516. 



-Chitin occurs in Peltigera canina and Evernia prunastre. 



3Cf. Miiller (11) and Ulander (26). 



^According to its behavior in sodium hydroxide solutions, the quantitative rela- 

 tions depending upon the source of the cellulose and the concentration of tlie solu- 

 tion. 



^Insolubility in dilute acids and alkalies; solubility in ammoniacal copper oxide 

 solutions; and production of a blue color with iodine and sulphuric acid. 



