CAR BOX SOURCES 



135 



Lenzites trabea, Merulius lacrymans, Polyporus betulinus, and Trametes 

 americana. 



The effect of a typical fungus causing white rot on the composition of 

 wood is given in Table 27. Polyporus pargamenus was allowed to act on 

 blocks of aspen wood for 20 months. At the end of this time the wood 

 block showed three degrees of attack. The tan-colored portion was 

 altered least. The pink-colored portion was intermediate, while the 

 white portion had lost the most lignin. P. pargamenus also degraded the 

 cellulose somewhat, as shown by lower degree of polymerization. 



T.\BLE 27. The Effect of Polyporus pargamenus ix Altering the Composition of 



Aspen Wood 

 Time of incubation 20 months. (Heuser et al., Arch. Biochem. 21, 1949. Published 

 by permission of Academic Press, Inc.) 



The effect of fungi causing brown rots on the composition of coniferous 

 woods has been studied by Schubert and Xord (1950). Lenzites saepiaria 

 in 13 months caused a decrease in cellulose in pine sawdust from 45.5 to 

 18.5 per cent. During this period the apparent lignin content increased 

 from 33.9 to 50.1 per cent. Similar results were obtained with Lentinus 

 lepideus and Poria vaillantii. For a recent review of the microbiological 

 degradation of cellulose see Nord and Vitucci (1948). 



Starch. Like cellulose, starch is a polymer of D-glucose. The glucose 

 residues are j oined through a-glycoside linkages, and starch (and glycogen) 

 may be thought of as consisting of repeating units of maltose. Starch 

 consists of two tj-pes of molecules. The linear portion of starch is called 

 amylose, while the branched-chain fraction is known as amylopectin. 

 Starch is sjTithesized by green plants, while glycogen is formed by 

 animals and fungi. The enzymes which catatyze the hydrolysis of starch 

 are known as amylases and were discussed in Chap. 4. The enzymatic 

 hj'drolysis of starch may be represented schematically as follows : starch -^ 

 dextrins— ^ maltose -^ D-glucose. The branched-chain dextrins are incom- 

 pletely hydrolyzed by amylase, while the straight-chain dextrins are 

 completely converted to maltose (]\Iyrback, 1948). 



Starch is insoluble in water. Only those furgi which produce amylase 

 are able to utilize starch. This ability is common among fungi but not 

 universal. Volkonsky (1934) found 26 isolates and species of the 



