200 THE CONSTITUENTS OF PLANTS. IX. 



it seems that the plan generally employed of determining 

 the "total pentoses and pentosans" by distillation with dilute 

 hydrochloric acid and precipitation of the furfuraldehyde as 

 osazone gives numbers which include these furfuroid sub- 

 stances described above and which probably possess greater 

 value as food stuffs than the pentoses and pentosans. 



Mannitol, Dulcitol, and Sorbitol are really alcohols and are 

 related to the hexoses as described under mannose. 



Perseitol is the alcohol corresponding to Manno-heptose, 

 C 7 H 14 7 . 



Lignose or Lignone (Cross and Bevan). Lignification is 

 the conversion of cellulose into woody fibre in the plant, a 

 change which greatly alters the physical properties of the 

 materials. According to Cross and Bevan this change is 

 accompanied by a chemical change which may be empirically 

 represented as loss of water 



2C fl H 10 5 = C, 2 H 18 9 + H 2 0. 



Cellulose. Ligno-cellulose. 



The ligno-cellulose, however, is, like cellulose, a highly com- 

 plex substance, and probably consists of a compound of 

 cellulose proper with lignone, an unsaturated substance con- 

 taining ketone and aldehyde groups. 



Ligno-cellulose therefore gives furfuraldehyde on treatment 

 with boiling hydrochloric acid and consequently probably con- 

 tains either pentosans or, more likely, furfuroids. 



The ligno-celluloses are probably partially digested by the 

 herbivora, and it is probable that the hippuric acid so charac- 

 teristic of the urine of these animals is derived from the 

 digested ligno-cellulose of their food. According to Cross and 

 Bevan* the process of lignification in a plant is characterised 

 by the formation of groups of the form 



C0< \CH 2 = C (i H H 5 



(OH) 2 (OH), 



Cellulose, 1895, p. 77. 



