162 AGRICULTURAL AND INDUSTRIAL BACTEKIOLOGY 



The celluloses, hemicelluloses and vegetable gums are 

 carbohydrates having very large molecules made up by the 

 polymerization of the simple sugar radicles. Inasmuch as 

 cellulose and hemicellulose and closely related compounds 

 constitute a large proportion of the bodies of the higher 

 plants, it is evident that were it not for the decomposition 

 brought about by microorganisms, there would be large 

 accumulations of such materials in soil. Many species of 

 molds and bacteria are known which can decompose cel- 

 lulose, breaking it down into simpler compounds. The 

 enzymes capable of bringing about these changes are 

 usually termed cytases or cellulases. A few organisms are 

 also known which can decompose vegetable gums which are 

 closely related chemically to the hemicelluloses. The devel- 

 opment of cytase by microorganisms may be demonstrated 

 by mixing finely pulverized cellulose or hemicellulose with 

 suitable melted agar, and pouring into a Petri dish. Bac- 

 teria or molds capable of digesting this carbohydrate will 

 be visible because of the clear ring surrounding the colony. 

 By the action of the cytase undoubtedly considerable quan- 

 tities of carbohydrate food are released to other soil bacteria, 

 not capable of attacking the cellulose directly. 



Pectinases are enzymes capable of dissolving or digesting 

 the carbohydratelike substance called pectin. This is present 

 in most plants, constituting the layer between the cellulose 

 walls of adjoining cells. In morphologic botany it is called 

 the middle lamella. It may be termed the glue which holds 

 plant cells together. "Certain microorganisms, particu- 

 larly among the molds and the bacteria, secrete pectinase 

 which dissolves this middle lamella and frees the cells from 

 each other. From an agricultural point of view this is par- 

 ticularly important in the retting of flax and hemp, in 

 which molds or bacteria dissolve out the pectins which bind 

 the linen 'fibers and hemp fibers together; it is important 

 also with certain of the disease-producing bacteria, such as 



