CHAPTER XXVI. 

 CELLULOSE-DECOMPOSING ORGANISMS. 



THE plant^residues which find their way into the soil contain, 

 in addition to protein, non-protein compounds. These are decom- 

 posed by microorganisms, thus liberating the energy and returning 

 the carbon to the atmosphere so that it is again available to plants. 

 The reactions occurring in this process are probably the reverse 

 of those occurring in the fixation of carbon by the plant. 



Plant 



C0 2 + H 2 



I 

 sugars 



1 



starches 



I 

 cellulose 



energy 

 absorbed 



r . .. 



Microorganisms 



CO 2 + H 2 O 



T 



sugars 



T 



starch 



T 



cellulose 



energy 

 liberated 



Cellulose. The term cellulose does not designate a single indi- 

 vidual compound but undoubtedly a whole series of compounds. 

 All of these are extremely complex and pass gradually from the 

 tender hemi- or pseudo-cellulose of the young plant, which is 

 comparatively soluble in acids and alkalies, to the more complex 

 and very resistant lignocelluloses. All are forms of cellulose, but 

 their properties are exceedingly different. The first may serve as 

 food even to man, but the latter is highly resistant to all the common 

 solvents. It is, however, dissolved by a few special solvents, such 

 as ammoniacal solutions of copper oxid, carbon bisulphid in sodium 

 hydroxid, and a few others. Cellulose is nitrogen-free and is 

 made up of carbon, hydrogen, and oxygen having the empirical 

 formula, (C 6 HioO 5 ) n . On hydrolysis, it yields various sugars, 

 depending upon its source, as glucose, mannose or xylose. In 

 the process of hydrolysis, there results certain intermediate 

 dextrin bodies, a study of which has shown cellulose to be ex- 

 tremely complex. Besides these there are certain gums, pectins, 

 lignins and similar compounds, which are nearly related to cellu- 

 lose and which have not been differentiated from the true cellulose 

 by many investigators. The results are that the power of decom- 

 posing cellulose has been attributed to certain organisms but a 

 careful study of the subject has revealed later that the organism 

 decomposed some of the related compounds but left cellulose 

 unaltered. 



Early Observations. That carbon passes through a definite cycle 

 from the solid organic tissues of plants to the gaseous form of the 



