GUMS, PECTINS, AND CELLULOSES 75 



rare cases, however, is there any evidence that they can be recon- 

 verted into carbohydrates to serve as food material. Certain 

 bacteria can make use of cellulose as food, and secrete an enzyme, 

 cytase, which aids in the hydrolysis of cellulose to sugars for this 

 purpose. But this enzyme seems rarely, if at all, to be present 

 in the tissues of higher plants. It has been reported that 

 some cellulose is hydrolyzed during the malting of barley, indi- 

 cating that this might have some food use for the growing seedling; 

 but this observation has not been confirmed and later investigations 

 seem to throw doubt upon its accuracy. 



Bacteria of decay also act upon cellulose materials, con- 

 verting them chiefly into gaseous products; but this seems to be 

 a provision of nature for the destruction of the cell-wall material 

 of dead plants, rather than an arrangement for the constructive 

 use of it as food for the bacterium. When fibrous plant residues 

 decay in the soil, the cellulose compounds are first converted into 

 a series of complex organic acids, known as " humins," which 

 undoubtedly have a significant effect upon the chemical and 

 physical properties of the soil, but these have little interest or 

 significance in a study of the chemistry of plant growth. 



REFERENCES 



ABDERHALDEN, E. " Biochemisches Handlexikon, Band 2, Gummisub- 

 stanzen, Hemicellulosen, Pflanzenschleimen ..." 729 pages, Berlin, 

 1911; ?nd "Band 8 1 Erganzungsband (same title as Band 2) ," 

 507 pages, Berlin, 1914. 



SCHWALBE, C. G. "Die Chemie der Cellulose," 665 pages, Berlin, 1911. 



